The dictionary does not comply with the most “recent” version of the portuguese language.
Here is a link to the orthographic accord: Portuguese Language Orthographic Agreement of 1990 - Wikipedia
I leave here an example:
the word “acção” became “ação” but the spellcheck only accepts the former aka the outdated spelling of the word
Keep in mind I’m giving only one example for brevity but the accord changed alot of details in the spelling of words in portuguese so it is, in my opinion, a very important “bug”.
With that being said, maybe being able to add custom dictionaries (textfiles with words on them) that are just wordlists could fix problems like this in the future. As far as I can tell, there is no grammar checking in place, only spellcheck.