In the Collabora Office there are some of the menus (so far I found that it is in number of words menu and in paragraph settings) in English even if the system environment is Czech and rest of the aplplication is in Czech too. Steps to reproduce (number of words): 1) in Android se Czech as a default language, 2) run CO - it should be in Czech, 3) open any text document 4) navigate to menu in the right upper corner, 5) tap on the menu "word count" 6) you will see that this sreen is in English System information: Model: Lenovo TB-7304F OS: Android System language: Czech App version: 6.4.3.
Currently only the core translation to a limited number of languages is bundled with the app due to size concerns. This can likely be worked around now that split APK is used for the app, but it has to be investigated and implemented, which will probably be done for the next version of the app. Since the bug was reported for Collabora Office, if you would like to follow up on this bug, please open a GH issue on the following link: https://github.com/CollaboraOnline/online/issues