BGB 616:
https://www.gesetze-im-internet.de/bgb/__616.html> Der zur Dienstleistung Verpflichtete wird des Anspruchs auf die Vergütung nicht dadurch verlustig, dass er für eine verhältnismäßig nicht erhebliche Zeit durch einen in seiner Person liegenden Grund ohne sein Verschulden an der Dienstleistung verhindert wird.
The key terms here are “verhältnismäßig nicht erhebliche Zeit” and “ohne Verschulden”. That means that if you’re absent a relatively short time (usually compared to the duration of the employment and the notice period) and without being at fault for the absence, you get paid.
There’s a lot of interpretation here: for example if your bus is late, you’re responsible (you could have taken an earlier bus), if there’s an announced strike, you’re still at fault - you knew before etc. The cause must also lie in your person specifically - if you’re stuck in traffic with hundreds of other employees due to an accident, the paragraph does not apply. If you’re missing out on work because you were involved in that accident, it does.
But being imprisoned without having committed a crime is very unlikely to be considered a fault of the employee.
Your work contract or collective bargaining agreement may modify or specify where this paragraph is applicable. No legal advice, not a lawyer,…