Language in the score for Tristan und Isolde

Here's a simple question that I might find the answer to more easily by asking than searching the internet for hours, what language did Wagner use when writing tempo markings and such in the original Tristan und Isolde score? I'd imagine German but I have this vague idea that Mahler was one of the first people to use German in his scores.

I would assume Wagner, since he spoke German, would have used German in his scores.

I know that Bach used German in his scores, which sort of refutes the idea that Mahler was the first composer to use German in his scores.

I would assume Wagner, since he spoke German, would have used German in his scores.

I know that Bach used German in his scores, which sort of refutes the idea that Mahler was the first composer to use German in his scores.

... Well, there are a lot of other composers that have used German in their scores before Mahler. So whoever proposed that either has no idea or is blind.

And, aaah, I don't know if he used German but I THINK he did, I haven't seen the actual score in a while so my memory is hazy.

It was written in German.