No, the reason you should (and not must) use escape codes is because the correct UTF conversion path gets lost between all the different encoding serializers from patch creator to svn repository, and so the text becomes garbage.
Another reason to use escape codes is that it makes the file ASCII-compatible and therefore readable in all known editors.
The only reason against it is raw size, which we don't care much about in Babble anyway, since it's quite the monster already.
I meant that it has to be "Mot de Pouvoir\194\160: Bouclier" and not "Mot de Pouvoir : Bouclier" because the people at Blizzard France that did the translation of "Power Word: Shield" used an editor that insert a "non breaking space" before the ":" as is mandatory in french.
Blizzard do not use escape code in their GlobalStrings.lua. In fact, the Blizzard translator are sometime a little careless about this and will have bizarre inconsistencies in the translation.
The non breaking space is one example of such inconsistency. For a long time, we had "Teleportation\194\160: Stormwind" and the like except for one "Portail : Thunder Bluff" that used a normal space, who knows why...
Another example is the "oe" character, Molten Core is translated as "Coeur du Magma", or more exactly "C\197\147ur du Magma". But there are plenty of items like the "Heart of Hakkar" that are translated as "Coeur d'Hakkar", not using the "oe" character.
A final example is the " ' ". Most of the time, it will appear as a normal " ' ". But there are a few exception, like "Cri d'intimidation", which becomes "Cri d\226\128\153intimidation".