First the page numbers. I had a minor "education" about this not long ago when someone said essentially what you have. I have just assumed that the "page numbers" in the stock reader were arbitrary. I was told "not so", that they followed some published "real book" version. Maybe. In any case, I eventually told the person that KoReader
can display "real" page numbers (as opposed to screen numbers), but only if the e-publisher includes that information. The "real" page number floats in the right margin.
Now to the dictionary. You may be in luck. Recently someone reposted a Spanish language dictionary for the 2015 Glowlight Plus on XDA after I had tried repeatedly to contact him and request a reup. You can read that post here:
https://forum.xda-developers.com/t/s...light.3554472/
But...I want to caution you about this. My work with making different dictionaries for the NST indicates that it is very important to kill the Reader process before swapping out dictionaries. If you fail to do this, you may "lose" space in /system. It's complicated to explain why, but suffice it to say, if you're using ADB anyway to install the alternate dictionary, the added step is easy. Otherwise, restoring a backup can fix the issue (so make a backup in any case before trying swapping dictionaries).
You can pm me if you want/need additional information.