Я немного говорю по-испански и по-немецки. -- I speak a little Spanish and German. The phrase "Я мало говорю по-испански" means that you don't speak too much, don't practice too much, don't spend too much time speaking Spanish. As for the second part of your question, if the noun follows "мало" (which is not your case) it takes the genitive form: мало времени, мало денег, мало проблем etc.

мало means that you not speak often or enough. Я немного говорю по-испански и по-немецки. in the second part of your question the word мало is not replaceable. You may change to genitive case only next word.

You must to use "немного". Я немного говорю по испански и по немецки.

я хорошо говорю по русски и мало-мало понимаю английский ( here мало-мало means just a few , really a few .