Changing Language of 1Password 8

You can change the language from within the app, that works already and is easy enough - as long as you can read the "incorrect" language sufficiently to be able to navigate the menus! It's under Settings / Advanced / Language (right below Security)

However it is still so, that the installer sets the language incorrectly if your regional format differs from your Windows display language. Software developers in English-speaking countries often don't seem to know how the locale settings work, and/or don't see that kind of thing as a high priority, so don't test the setups you typically find in non English-speaking countries.

Some software and websites don't even allow you to choose the country and the language independently, but only support the official languages of each country. Spotify, for example! That is a huge pain. At least 1password doesn't have that problem.