Yes, you can.
You can offer more than one language if you grew up bi- or multilingual, or if you went to school or studied in that language. In general, we only match native speakers or near-native speakers with each other.
You can also search for a tandem partner in more than one language. In this case, please fill out the online registration form for each language. If you fill them out consecutively, your information will be saved in the form.
However, please make sure that you have enough time to meet with more than one tandem partner on a regular basis.