language pack po mo not working

Dear sir, I found the Chinese zh_TW language translation is quite good (but all entries are pending since 6 months ago) so I tried to compile the lanaguage PO file my self https://prnt.sc/hcoocb . I have used PO editor to compile them to MO and uploaded to wp-content/languages/plugins with filename: bbp-messages-zh-TW.po and .mo
but the plugin still show in english (the site has been set to zh_TW and you can see the bbp translation is working) https://prnt.sc/hcooke
could I ask any steps I missed to make the translation for bbp-message working?
it is a really good plugin!
thank you!