Given the improvements in i18n/L10n for the Installation System in being able to select the language the administrator installs phpBB3 in, this enhancement should be replicated within "core" phpBB3 if impact is minimal. I believe there are two levels of support in which how this could be fixed.

Full fix: Replicate the Installation System language selector within the forum itself, so guest users can also select an installed language (other than the forced default, as is the case currently). This will allow the user to be able to register in their native/preferred language, and not have to "navigate blind" as they would currently have to do in phpBB2 and phpBB3 CVS.

Partial fix: Given the above may be too invasive to add at this "late" stage, a suitable workaround would be to move the language selection at registration to be moved forwards to the Registration Agreement screen. This would at least allow the user to view the agreement in their native/preferred language, which would then carry over as the default selected language should they choose to accept and go through the registration process.