Is there in fantasy literature any character with a reputation for being an accomplished thief with a rudimentary knowledge of magic other than Fritz Leiber's Grey Mouser? Let me amend that question. Is there in any work of fantasy literature predating Dungeons & Dragons such a character that would explain the existence of the thief's ability to Read Languages (and magic scrolls)?
As far as I know, the Grey Mouser is the sole reason for this particular thief function, which is a tad preposterous considering that a) the Grey Mouser was the exception to the rule, and b) his limited magical ability came from his aborted apprenticeship with a hedge wizard, i.e. he was a dual class magic-user/thief who switched classes after 1st or 2nd level (per "The Character With Two Classes" on page 33 of the 1st edition Players Handbook).
Of all the classes in traditional D&D, the thief would probably be the least likely to have any sort of skill in either cryptanalysis or "decoding" writing in foreign languages. This might be a plausible skill for the thief-equivalent specialist class in Lamentations of the Flame Princess. For the typical uneducated pickpocket, basic literacy would be a rare ability. If any of the classes have an affinity for writing and interpretation of meaning, it would be magic-users, clerics, and monks. Just because thieves can communicate in their own secret jargon (Thieves' Cant) doesn't mean they have the scholarly training and resources to read a scroll in a foreign language they don't even speak (or that they can read at all). To suggest that thieves would have an ability beyond even that of sages to cast spells from scrolls is, frankly, absurd.
Instead of the Read Languages ability, I have ruled that in my games thieves may develop their Encode or Decode skill. This is a skill that enables a literate thief to convert writing in any language he or she knows to a secret code, and to comprehend encoded writing in any such language. If the thief doesn't know the language, he or she will be unable to decode or read it. In my house rules, thieves may choose which thiefly skills will increase as they gain levels (as in LotFP), so thieves who lack interest (or the ability to read) would concentrate on other skills, whereas those more concerned with esoteric treasure-hunting or espionage would be free to increase their Encode or Decode skill at a rate of their choosing.
That solves my problem, but I am still curious to know if there are other literary examples of the thief with extraordinary language skills and limited spellcasting ability.