The most important subjects for the guide is in English, because it requires talking to foreign tourists, and English is the lingua franca of the world, no matter what language is used, each is a national language.
For a guide to the most important subjects is English because it requires talking with foreign visitors. And English as the lingua franca of the world no matter what language is used, each national language.
Most important subjects for a tour guide is an English because of the need to use to talk to foreign tourists And the English as a lingua franca world whether each will use what language is the national language.