There can be more than one person working on the same translation. Of course, all translators working on the same language pages will be informed about each other's presence.
In case of multiple translators, it is important that it is clear to everyone involved who is translating which part. Communication can go through me or directly between the translators.
PmWiki has support for handling the case where multiple authors attempt to edit the same page simultaneously. See Simultaneous Edits for an explanation of this feature.