Conclusion: English is the most recommendable for most people. But in the case of native speakers of, for example, Spanish, Portuguese, and Chinese, the languages to use may be different.
Related contents:
1. The documents used in this episode.
- List of languages by total number of speakers
- Languages of Europe
2. Note 136 Recommendable education materials for learning foreign languages
3. Note 063 Which languages are recommendable to study?
4. The video version of this episode: [Note 134] Which language is recommendable to broadcast on YouTube?
