It seems that on gTTS there is no option for changing the speech of the text-to-speech apart from the slow argument.

I would like to speed up the sound by 5%. Any suggestion on how I can do it?

Best.

tts_de = gTTS("Hallo, guten tag.", lang = 'de')
tts_de.save("s.mp3")

This isn't actually possible. According to the offical gTTS docs, the only arguments relating to speed gTTS accepts is slow, a boolean specifying whether or not to slow down the playback.

If you're playing the file through Python, however, I'm sure there is a module that supports sped-up playback.