Hi steppenwolf,
In this post, I answered a question regarding computation of facet vectors, including tangential facet vectors. There I have linked to this gist which has dolfinx code that computes tangential facet vectors in such a way that all the tangent vectors are “oriented in the same way”, e.g. such that all have a positive x component.
That code also includes normalization of the tangent vectors, such that their length equal unity.
Let me know if this solves your problem.
Cheers, H