Regular replacement useed:

TYPO3.lang.<some_key>¶

S: TYPO3\.lang\.([a-zA-Z0-9_]+)
R: TYPO3.l10n.localize('$1')

Replaced it manually because at the beginning, there's a file where I should use double quotes instead of single ones to avoid having to escape them in a big raw inline JS.

TYPO3.lang['<some_key>']¶

S: TYPO3\.lang\[([^]]+)\]
R: TYPO3.l10n.localize($1)

This tackle with single/double quote as well, if needed. And other cases such as TYPO3.lang['<some_key_prefix>' + suffix]

Patch set 1 of change I68f968df3f3d105ee566987c000e3dafb97b9fe3 has been pushed to the review server.
It is available at http://review.typo3.org/4388

Patch set 2 of change I68f968df3f3d105ee566987c000e3dafb97b9fe3 has been pushed to the review server.
It is available at http://review.typo3.org/4388