An interesting question on SoftwareEngineering on StackOverflow discusses Ubiquitous Language in a non-English domain. They note three options:

1. Fully use the natural language of the domain.
2. Fully work in english only.
3. Create a translation table, use english internally, and the natural language outwards.

The original asker reports that about a year later, they made good experience with the third option. Translation is not an issue, and explicit translation has even helped to think about the domain more.

Answers highlight the difficulty of this decision. ZioBrando notes that the Ubiquitous Language is just a tool: If you don’t have an issue with translation or understanding, there is no need to fix anything.

PierreHenry notes a project in Switzerland that used mixed-language code base, and considers that the right decision, as much of the domain language was untranslatable.