As well as setting preferred browsing languages for extra practice, it’s also a good idea to put the browser itself into your target language to get a little bit more exposure.
With Firefox, this is pretty straightforward. You don’t have to go the length of downloading and installing a separate version of the software - you just need to get the relevant language pack.
The first thing to do is go to this list of Firefox language packs and select the XPI/s you want. Some suggestions:
Chinese: zh-CN.xpi, zh-TW.xpi
You’ll get the usual yellow prompt to allow installation.
Then another window to confirm it again.
Then enter about:config into the address bar, and confirm that you’ll be careful. In the ‘Filter’ field, enter _general.useragent.locale _. Double click on the line that’s there, and type the locale you want in the dialogue that pops up (e.g. zh, ja or ko).