我不但会说中国话还会说德国话和美国话。 I can speak not only Chinese but also German and American English. "a country + 话" means the language that most people used in the country 中国(China) 中国话Chinese 德国(Germany) 德国话German 美国(American) 美国话American English But we don't really use this way to say languages very often. We just say 汉语/中文 which means Mandarin. 英语English British English英式英语 American English美式英语 德语German 不但……而且/还…… 不仅……而且/还…… They just like "not only... but also..." in English, a fixed thing. Maybe someone sent this to you just want to be language partners with you, but as you feel, you are not sure what he/she want to say exactly in the sentence. But the sentence is OK and nice. 我不但会说中国话(，)还会说德国话和美国话。 Yeah also you can add a comma there, this made the sentence much easier to understand.

this means: he can speak not only Chinese but also German and American English. I am a TCSOL, I can help you with your Chinese, if you want, you can contact me and we can progress your Chinese.

I don't think it is written by someone who knows Chinese well. For example "美国话" is rarely if not never used. As such, it is very hard to tell if the person meant to be friendly or provocative. I wouldn't assume that there is any underlying tone to the sentence.

Ich kann nicht nur Chinesisch sprechen, sondern auch Deutsch und Englisch. Aber 美国话 und 德国话 sprechen wir Chinese sehr selten, wir sagen 英语(美国话) und 德语(德国话).