BuddyPress.org

Test it with just WordPress installed … BuddyPress de-activated.

Can you change the permalinks to a custom structure e.g. /%category%/%postname%/ and still view pages / categories without problem?

You need WordPress working correctly with permalinks.

If that’s OK, then install / activate BuddyPress, select the BuddyPress default theme, and check everything works.

Once you’ve done this, you can install your language packs, plugins, etc.