Short form: you tell them you are leaving in order to expand your experience and skills. As for your successor, you don't need to leave anything beyond whatever documentation/reports/memo you have produced.
Long form: Programming, unlike most professions, is in part defined by the tools one uses. Both managers and HR understand this (even those asking for 5-7 years of Go experience), neither will blink at hearing you want to expand your experience. That you want to work with a specific tool or simply to vary your experience will be taken as neither rejection or signs of unreliability. Everything else being equal, experience with more languages, frameworks, editors, IDEs is a plus - it gives you a yardstick for comparison, making your judgement more worthwhile.
You don't say whether you have tried to convince your current employer to switch tools or whether you even think it would be a good idea for them to do so. If you do and have, then your boss should already have everything your replacement needs if the decision is revisited, it's not your place to try to convince them to take up the cause in your place.
What you should be leaving for your replacement is as much documentation about how to do your job as you have available. If you feel that there is something you know about how to do the job with the current tools, that your replacement should not be expected to know or easily discover, then document it.
As for your complaints. You should not be mentioning them at all, they aren't relevant.