The themes are linked to the interface language - the filters data being different according to the languages. If you wish to create the same theme in 2 languages, you will have to create it independently for each language.

https://s3-us-west-2.amazonaws.com/secure.notion-static.com/88793d30-055e-42b2-9c5b-046447a796cd/I_changed_the_language_of_my_interface_and_I_cant_find_my_themes_anymore..gif