In File > Options > Editor
NB: Finnish is not well supported by Hunspell, so Finnish linguists should use the MS Word spellchecker instead:
In the AutoCorrect settings, do customise as you prefer. More information in Studio 2021 help: SDL Trados Studio 2021 > Translating documents > Setting preferences for translation > Autocorrect
Here in Languages, select your own languages:
In File > Options > Verification