I'm not sure why, I've checked the text2.txt file numerous times and even re-written the string names. All my other string definitions work, but nothing will show up in those speech-boxes.
IIRC I once had the same problem and it appeared to be related to the string ID's length (being too long). Try something like IDS_ALD_BGN instead of IDS_ALLIED_BEGIN and see if it helps.
Also, are you adding _BHEAD0TEXT at the end of the ID in the text2.txt file when using the "BattleHead0" popup? So that should be:
IDS_ALLIED_BEGIN_BHEAD0TEXT, "blah"
not
IDS_ALLIED_BEGIN, "blah"
(note: I'm not looking at the files at so i'm not 100% sure it's "_BHEAD0TEXT". Just take a look at examples in the other text2 files.)