Subjunctive mood usually starts with if. It seems: If you are happy/if you were happy (both are right) If you were me (right) / if you are me (wrong) If you want to learn English / if you wanted to learn English (which is right?) Which is subjunctive mood?
1: If you want to learn English, ELL is the site to use.
2: If you wanted to learn English, ELL would be the site to use.
I couldn't really argue with anyone who wanted to swap is / would be in those examples. The versions as given are certainly more likely, but it's not obvious to me that the alternatives would be "ungrammatical".
But consider a context like ringing through to room service in a hotel, where the person who answers might say...
[Hotel reception speaking...]
3: ... what do you want?
4: ... what did you want?
Both Present and "Past" are perfectly idiomatic there, but I've used "scare quotes" because I see no good reason to classify my example #4 as being significantly different to #2.
Maybe some people would say #2 is "Subjunctive", whereas #4 is "Past", but that doesn't seem a useful distinction to me.
I think English only really has 2 tenses (Present and "Not-Present"), and #4 is a typical example of "Not-Present" being used to "distance" the speaker from the utterance (introducing "hesitance, deference", characteristic of many formal contexts). A bit like asking Who might you be? rather than Who are you?, for example.
TL:DR: Using "Not-Present" verb forms in English doesn't necessarily have anything to do with time-based relationships. Example #2 above is just a common way of making the assertion more "politely tentative" (arguably implying more strongly than #1 that perhaps you might not want to learn English anyway).