I think ttf yes, look for similar tutorials for ps3
with vita is is dangerous because we don't have much protection.
maybe we can restore from a bad font... I don't know.
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oops, it's not ttf I think...
in sa0:/data/font - I see pgf files... like psp.
http://www.consolespot.net/forums/psp-help-tutorials/14396-how-convert-ttf-font-pgf-fonts.html
good luck