1. I'm confused at how you have skill and learn as the variable names instead of language and languagelearning?" - He means in the Query Filter
As you will know, you can set anything as the variable in a Query Filter.
I just chose those as they seemed more simple for me to make the test.
You could also put "paramone" or "whateveryouwant"
The important is, the Code the generates the URL is actually matching this variable.
2. Also, where is this capital letter designation you speak of? The programmer says "uppercase letters don't matter because we're using a like query which doesn't care about case" ?
You do store Capital (Upper case) value in the Database, this is clearly visible in the Toolset > Post Fields > your_group > your_field > Value to store
if you store Upper Case Values, then the URL param must of course match this as it searches for the value in the Database.
You store Upper case, as visible in the above mentioned settings, and as you will see, the View I created for you, works fine if you query by Upper case terms but not if you query by lower case.
This is case sensitive.
3. I have replaced all "language" to "skill", as well as "languagelearning" to "learn"
As said, it does not matter what is your variable, it just must be the same when you call it.
It means, if you set the variable "myvariable" in the Query Filter, the URL you call must of course end with:
? myvariable=whateveryoursearchfor
4. The programmer says "all my code is doing is taking selected form values and putting them into the url"
Yes, but probably not the correct values.
I will nto anlade this code, but if the Code produces URL's matching the variable AND the value as exact in the Database AND the user has this information stored, it will return by the View, as you can se in the View I set up for you, which works fine with Types 2.0.1
5. How do I test if it's a "corrupted view" – simply create a new one, using the same parameters and code?
It would be the fastest.
It would take 10 minutes to set a new View and make some manual tests, as suggested earlier, introducing one query after anther and outputting information as in my test view which helps you as well to see, how many results are produced, the ID's of the users, where are empty and not empty fields, etc.
Then you can still copy and paste over the HTML, in case this is a View corruption.
But I assume the issue relies within how the values are passed (upper and lower case as example)
Thank you