You haven't done anything wrong with that OXCE+ install, that's the perfect way to do it! To get the strings, you can either search for them in Piratez_lang.rul from Piratez and create a mod just for the missing strings, or re-write the strings yourself in a mod. All you need is a ruleset file that looks like
extraStrings:
- type: en-US #or whichever language file you're using
strings:
STR_NAME_OF_MISSING_STRING_1: "Whatever the text is supposed to be"
STR_MISSING_STRING_2: "Lorem Ipsum"
#... and so on until you get all the strings
And yes, you should be able to access the saves from the openxcom 1.0 install, but you shouldn't try to load more recent saves into 1.0. If you want to use a different users folder, you have to specify that with a command line option - I use that to help keep saves from different mods/settings separate.