Some custom translation is not updating

The translation in my native language (Thai - th) is not completed so I want to update it by myself without having to go through the Transifex process.

So far, I have followed the instruction in this document - Adding custom translations but I only succeeded to translate some of them. There are some msgid which although I have already changed the translation in the *.po file, they do not get updated.

I running a forked of ed-platform so I have tried changing both *.po files under conf/locale/th/LC_MESSAGES (in my forked ed-platform) and env/build/openedx/locale/th/LC_MESSAGES (in tutor root), but neither of them is working.

Has anyone ever faced this same problem?