"I speak Swedish."
Translation:Jag talar svenska.
Verbs belong to different groups that behave a little differently. Take a look at this page, it's a start: https://www.duolingo.com/skill/sv/Verbs%3A-Present
svenska is the noun denoting the language (or a Swedish woman).
The adjective has the forms svensk, svenskt, svenska and svenske.
The form of the adjective ending in e can only be used about males. It is never necessary to use it, you can always say svenska instead. We usually say den svenske kocken 'the Swedish chef' but den svenska kocken is also correct.