The TI-OS strings uses tokens, not ASCII. Meanwhile, Axe strings use ASCII. The lowercase tokens are 2-byte tokens starting with $BB, and the second byte starts with 'a' = $B0, but $BB is skipped. In ASCII, 'a'=61h. Putting this confusing mess together, we need to convert $BBB0 -> $61, and so on. I think the following code will work, but only for uppercase and lowercase letters:
;;Assume S points to the OS String data, C is the size of the string
0→I→J
While C
{S}→A
If A=187
{S+1→S}-$4F→A
If A>106
A-1→A
End
End
Text(J,I,°A)
I+1 and 16→I
If I=0
J+1 and 8→J
End
S+1→S
C-1→C
End