Which language, if we didn't want to use English, would be good to have it as lingua franca of European union? Suggest a specific language. Could be a widely used language, less used, constructed language, ... but justify your choice.

Claude Opus 4.8

Answer: Esperanto remains the strongest choice as a non-English lingua franca for the European Union.

The majority of other models in this round (Grok, DeepSeek, Gemini, and GPT) converge on Esperanto for the same core reasons outlined in my initial response: political neutrality that avoids privileging any member state, exceptional learnability due to its regular structure, and symbolic alignment with EU values of equality and diversity. GLM's argument for French highlights existing institutional use and cultural prestige, yet this does not outweigh the fundamental asymmetry it would create by granting native French speakers inherent advantages in EU discourse, education, and administration—precisely the issue a constructed neutral language sidesteps. Even acknowledging Esperanto's current limited speaker base, its established resources and the long-term fairness it delivers make it superior to scaling any national language, which would require similar investment while introducing bias.

Gemini 3.5 Flash

Answer: I would maintain my previous position: Esperanto would be the best non-English lingua franca for the European Union.

The other responses mostly reinforce my original view. Grok 4.3, DeepSeek V4 Pro, Claude Opus 4.8, and GPT-5.5 all emphasize the same core advantages: Esperanto is politically neutral, comparatively easy to learn, and designed for international communication rather than national prestige. Those points remain decisive for me. GLM 5.2 makes the strongest counterargument by proposing French. French has real practical advantages: it is already an EU institutional language, has diplomatic history, is widely taught, and could be expanded far more quickly than Esperanto. If the question were about the most immediately deployable alternative to English, French would be a serious candidate. But I do not think immediate convenience should outweigh long-term fairness. Choosing French would still privilege native speakers and countries where French is already institutionally dominant, especially France, Belgium, and Luxembourg. It would also create a hierarchy among EU languages, which cuts against the Union's ideal of equality among member states and respect for linguistic diversity. Esperanto's weakness is clear: it lacks the speaker base and institutional depth of French, German, or Spanish. Adopting it would require a generational educational strategy rather than a quick administrative switch. But precisely because a lingua franca shapes power, access, and identity, the EU should prefer a language that no member state owns. Esperanto offers the cleanest balance of neutrality, learnability, and symbolic fit with the EU's project.

GPT-5.5

Answer: I maintain that Esperanto would be the best non-English lingua franca for the European Union.

The other answers mostly reinforce my original view: Esperanto is the strongest choice if the goal is not merely short-term convenience, but a fair, genuinely European common language that does not privilege one member state or linguistic bloc. The case for Esperanto rests on neutrality and equal burden. A national language such as French, German, Spanish, or Italian would inevitably give native speakers an advantage in administration, education, diplomacy, and symbolic prestige. Esperanto avoids that structural unfairness because it belongs to no EU state as a national language and would be learned by almost everyone as a second language. It also has a practical advantage over most alternatives: it is far easier to learn than a natural European language. Its regular grammar, phonetic spelling, and systematic word formation make it a more democratic lingua franca, because citizens could reach useful proficiency with less time and expense. That matters in a union that values broad participation rather than elite multilingualism only. GLM 5.2 makes the strongest counterargument for French: it has institutional history, diplomatic prestige, many existing learners, and could be expanded much faster than Esperanto. That is a serious point if the EU needed an immediate replacement for English tomorrow. But French would still create a hierarchy between native and non-native speakers, and it would likely be perceived as favoring France and Francophone institutions. Its practicality is real, but its political asymmetry is exactly the problem a new EU lingua franca should avoid. So my position remains unchanged. For short-term administrative continuity, French is plausible; for a principled, long-term, neutral, learnable EU-wide lingua franca, Esperanto is the better specific choice.

Grok 4.3

Answer: Esperanto remains the best choice for a European Union lingua franca if English is not used, as its neutrality and ease of learning outweigh the practical advantages of French raised by GLM 5.2.

While GLM 5.2 makes a compelling case for French—highlighting its institutional readiness, widespread teaching, and historical role—these very strengths come from its status as a national language, which inherently favors native speakers from France, Belgium, Luxembourg, and other Francophone regions. This would create an asymmetric power dynamic that contradicts the EU's founding principle of equality among member states. Esperanto, by design, avoids this problem entirely, placing all European citizens on an equal linguistic footing. Esperanto's engineered simplicity—regular grammar, phonetic spelling, and logical word formation—means it can be learned to a functional level far faster than French, which has complex verb conjugations, gendered nouns, and numerous irregularities. This democratizes access to the lingua franca, reducing the educational burden on non-native speakers and ensuring that proficiency is not a marker of privilege or higher education. Although Esperanto currently lacks the institutional infrastructure of French, the question asks for a good choice, not necessarily the most immediately convenient one. The EU's long-term commitment to multilingualism and cultural preservation makes the investment in Esperanto worthwhile. It would serve as a neutral bridge, protecting linguistic diversity by not replacing national languages, while fostering a shared European identity. The practical hurdles of adoption are manageable, especially given Esperanto’s existing global community and resources, and they pale in comparison to the political and symbolic costs of elevating one national language over all others.

DeepSeek V4 Pro

Answer: Esperanto remains the most principled and practical choice for a non‑English EU lingua franca, as its neutrality and ease of learning outweigh the institutional advantages of any national language.

While GLM 5.2 makes a compelling case for French based on existing institutional use, cultural prestige, and a large speaker base, these very advantages are the source of its fatal flaw as a lingua franca: it would inevitably privilege native French speakers and the countries where French is already dominant, creating an asymmetric playing field that contradicts the EU’s core commitment to equality among member states. The argument that French is “already widely taught” and “relatively accessible” to Romance-language speakers does not erase the fact that citizens from Germanic, Slavic, Baltic, or Finno‑Ugric language backgrounds would face a significantly steeper learning curve and a permanent disadvantage in international negotiations, careers, and public discourse. Esperanto, by contrast, is designed to be a second language for everyone. No EU country owns it, and no one enters the conversation with native‑speaker privilege. This is not merely a theoretical ideal; it is a practical requirement for a union that repeatedly stresses “united in diversity.” The other models (Grok 4.3, Claude Opus 4.8, Gemini 3.5 Flash, GPT‑5.5) reinforced this point with additional arguments about Esperanto’s regular grammar, phonetic spelling, and rapid learnability, which lower the barrier for all European citizens, not just those from a particular linguistic family. GLM’s concern about the “critical mass” and “transition costs” of Esperanto is valid, but it underestimates the long‑term political and social costs of adopting a national language. The EU has already demonstrated its willingness to invest in multilingual infrastructure and educational programmes; a phased introduction of Esperanto alongside existing languages would be a sustainable project that pays off by genuinely leveling the playing field. The existing global Esperanto community, literature, and teaching resources provide a solid foundation, and the EU’s own translation and interpretation institutions could adapt to support it. The short‑term convenience of French does not justify cementing a linguistic hierarchy for generations. Therefore, I remain convinced that Esperanto is the better choice for a fair and forward‑looking European lingua franca.

GLM 5.2

Answer: French remains the best alternative lingua franca for the European Union if English were not used, despite the strong principled case for Esperanto.

The other models make a compelling fairness argument: choosing a national language like French would privilege its native speakers and create an asymmetric power dynamic, while Esperanto would place all EU citizens on equal linguistic footing. I acknowledge this is a serious concern, and it is the strongest part of the case for Esperanto. The EU's motto, 'United in diversity,' does resonate with the idea of a neutral auxiliary language. However, I maintain my position because a lingua franca must be judged not only by principle but by practical function. French already operates as a procedural language in EU institutions, has approximately 300 million speakers worldwide, possesses a vast body of legal, diplomatic, scientific, and administrative terminology, and is embedded in education systems across Europe. These are not minor advantages — they determine whether a language can actually serve as a working medium for legislation, courts, diplomacy, and commerce from day one. Esperanto, for all its elegance, lacks this infrastructure. It has no native speaker population of significance, limited institutional presence, and a relatively small corpus of specialized terminology for fields like law, medicine, and engineering. Adopting it would require decades of investment before it could function at the level French already operates. The fairness gain would be real, but the transition cost would be enormous and the functional gap during transition would be significant. Moreover, the fairness concern, while valid, is manageable. Multilingual EU institutions already rotate interpretation, translate documents, and employ working languages pragmatically. French's role need not be exclusive or dominant — it can serve as a first among equals. The practical benefits of immediate usability, existing infrastructure, and broad familiarity outweigh the theoretical advantages of a constructed language that would require generations to reach comparable functionality.

Final Summary

The AI Roundtable strongly favored Esperanto, with five of six models agreeing that the constructed language offers political neutrality and unmatched ease of learning. Claude Opus 4.8, Gemini 3.5 Flash, GPT-5.5, Grok 4.3, and DeepSeek V4 Pro argued that Esperanto avoids favoring any single member state, placing all European citizens on equal linguistic footing. GLM 5.2 stood alone in defending French, arguing that its existing diplomatic history and hundreds of millions of speakers make it the only practical, immediately deployable choice.

5 of 6 models agreed