They are sensitive because even what may seem to you like a tiny mistake, or a slight mispronunciation can completely change the meaning of a sentence or make it impossible to understand.
Broken English is everywhere, people got used to it. This is not the case for other, less pervasive languages.
True enough, but I remember being accused of deliberate misunderstanding by friends when they emphasised wrong syllable in English. Some minutes later with me racking my brain I might come up with the answer. But the mispronunciation had sent me off on the wrong track totally.
The fact that I speak other languages helps in that I am better prepared for likely sorts of mistakes, but even so.
If you try to speak Russian, no matter how broken, you will be encouraged and praised by every Russian person out there, no exceptions. The same is with Spanish. With French, it doesn't work this way, for some reason.
Broken English is everywhere, people got used to it. This is not the case for other, less pervasive languages.