I use my manjaro in pt and noticed that the plasma and qt applications are translated into my language but several parts are still in english, I researched and found nothing about it tip? Thank you
You should be specific when you mention “several parts”.
And in those cases best road to walk is to report it to that application’s developers/maintainers.
(I’m lucky to be able to use 4-5 languages in real life, among which english is foreign for me also 
)
some menus are still in english mixed with portuguese, the dolphin even has about 20% of its functions without translating, is there no package to try to reinstall and see what happens?