Like countries such as Canada, Ireland, New Zealand or Belgium, Grennia operates in a bilingual manner, with both English and Japanese being official languages.
However, English tends to be more dominant overall.

The rules for what should always be bilingual are laid out in the Bilingual Act (2005), a law in Grennia which dictates what should always be bilingual.

Bilingual requirements are imposed for:
- Food packaging and nutrition labels
- Road and traffic signage
- Official government announcements (especially those of the Prime Minister)
- All Members of Parliament should be trained in both languages, being able to pass both Band 9 of IELTS for English and the JLPT N1 for Japanese
- Both English and Japanese are mandatory school subjects for all 12 years of compulsory education

In all other cases, English is primarily used.

Additionally, the sign language used in Grennia is British Sign Language (BSL), taught in all schools which provide learning for the deaf community and used amongst non-deaf sign language learners.