Which language should I learn

Hello- my university offers cheap Language courses. I already have learnt conversational Spanish, and need to know what I should go for next.
The choices are:
Arabic
British Sign Language
French
German
Italian
Japanese
Mandarin
Polish
Russian

Considering Polish atm, but have heard it is ridiculously hard.

German is fucking hard to learn.
Normally, you need to learn a fuckton of rules to learn a new language... German has no rules. Almost EVERY SINGLE WORD is irregular.