That's mostly for police. Once you're in court and ordered to testify, the person talking about germany is mostly correct. You can't be forced to self-incriminate nor testify against a spouse. Otherwise yes. Generally 99% of courts won't bother even asking the defendant to testify because self-incrimination is practically guaranteed. Usually only if the defense calls on them, which is often a bad idea.

Only if there’s a risk at incriminating yourself, and if it’s not immediately apparent how you’d run that risk (e.g. you’re a witness that doesn’t have a direct relation to the crime at hand) you’d have to motivate how it could be incriminating.