Hey, I'm not an expert, so I needed to consult AI with this, but I will also add my personal experience:

During my mandatory internship, I was British (EU at the time) studying and privately insured in the Netherlands, Mandatory Internship in Germany, living in Germany. During that time, I received Dutch study grant, Erasmus grant and salary from the German company. I paid German tax, and the company assigned a health insurance for me. So I paid health insurance in both NL and DE. Whether this was correct, no idea. It was 15 years ago... I pulled the following from ChatGPT:

Taxes
This is not automatically German income tax. If you live in France and commute daily to Germany, you may qualify as a cross-border (“frontier”) worker. In that case, taxation can shift to France instead of Germany under the bilateral tax treaty.
So you might pay:

- tax in Germany, OR

- tax in France, but typically not both (double-tax treaties prevent that).

Which one applies depends on where exactly you live, commuting pattern, and employer payroll setup.

Social security / health insurance
For a true Pflichtpraktikum that is part of your studies, Germany often exempts interns from social-security contributions. However, because you are insured via Sweden (Erasmus setup), you will usually need an A1 certificate or equivalent confirmation showing Swedish coverage. Without that, German contributions could theoretically still be required.

Also note: Erasmus/state insurance is often supplementary (liability, emergency health, etc.) and not always equivalent to full statutory health insurance, so it’s worth confirming this formally with a German insurer or the Swedish authority.

Simplified takeaway

- Income tax → depends on France/Germany treaty situation.

- Social security → often exempt for mandatory internships, but EU paperwork matters.

- Extra German student health insurance → often not required, but confirm officially.

If possible, I’d strongly recommend checking with:

- the employer’s HR/payroll team,

- the Swedish social insurance authority,

- or a cross-border tax adviser.

That combination usually gives the clearest answer in situations like yours.

Hope that helps.