I think there is something unconsistent between the msgid "+ Expand All" (and "- Collapse All") and the way it's used in "themes-ai1ec/vortex/agenda.php"
It's called with _e( 'Expand All', AI1EC_PLUGIN_NAME )
I guess it should be _e('+ Expand....
The i18n isn't working for these 2 messages.
I tried to change it to _e('+ Expand All' with no success
I then modified my localized version (fr_FR .po file + msgfmt => .mo) in order to have the msgid without the + and - signs.
I hope my explanations are clear enough. first time I play with _e, .po, .mo stuff.
By the way, I think the msgid "Day" & "Week" are missing, too. At least in the fr_FR.po