Mould in sublet room: advice?

Advice needed for a foreigner about housing situation: I am subletting a room from my roommate (who is in contact with the landlord). Two months ago I told my roommate that there is moisture and developing mould in my room, and to tell the landlord. I provided pictures. The moisture is not my fault, when it rains I often also see water being pressed in from the outside. So far nothing has happened, the mould just got stronger. I have the feeling that my roommate doesn't care because the other rooms are not affected. Where I come from I could absolutely legally refuse to pay rent (or insist on a deduction) if the landlord does nothing about it. I am considering searching for a new place of course. But I also want to know if it's common practice here to withhold paying the rent until things are fixed and if I can force my roommate's hand (who receives my share of the rent) so that they in turn force the landlord's hand. Does anyone have experience with issues like these?