Hi Sander,
Of course you are right, and this is why PixInsight, our entire website, and the official documentation (both the existing documentation for PixInsight LE and the documentation that we are writing for PixInsight Standard), are originally published in English.
Most processing tutorials on our website are also in English, and in fact not all of them have been translated into Spanish (due to lack of time).
However, please realize that while we recommend that all authors make translations of their tutorials and examples into English on a regular basis, along with other languages that are important (numerically) among our community --mostly Spanish and French--, we cannot force them to do so, and in many cases they don't have the time and/or resources to perform the required translations.
Having said that, I want to stress that you're absolutely right: to maximize global diffusion of all authored works, it is advisable to publish, as long as possible, English and French translations.