New people, new country, new culture, new language - a stay abroad during your studies is not mandatory, but highly recommended. In addition to broadening one's horizons, such an endeavour also enriches one's resume and academic and language skills.
It is impossible to say when the right time for one or more semesters abroad has come. In principle, it doesn't seem to fit optimally anywhere within the packed bachelor's and master's degree programs. That's why we can't make a good recommendation for it.
In any case, you should think about it very early and, depending on where and/or with which program you want to go abroad, start organizing up to 1 or even 2 years in advance. Especially for completely foreign languages, you should plan several semesters for language courses.
Although it is of course possible to study abroad at a foreign university as a free mover or without a program, the effort, financing, etc. is much more relaxed with a program. Especially accruing tuition fees etc. are usually financed by a program or the home university.
If you want to study abroad or if you come from abroad and want to study in Karlsruhe, you will find useful information at the
International Students Office (IStO)
Campus Süd, Gebäude: 50.20, Raum 106
Tel.: +49 721 608-44911
Webseite: https://www.intl.kit.edu/isto.php (Currently, they don't have an english website.)
Specific Information regarding physics are on the faculties website, including the German-French double master with Grenoble. Prof Dr Pilawa is responsible for the exchange programs at the Faculty of Physics.