#: ../pitivi/check.py:130
"Please use a version of the Python bindings for GTK+ built with Cairo "
"support."
#: ../pitivi/check.py:148
"You do not have a recent enough version of the GTK+ Python Bindings "
"(currently %s)"

"Python bindings for GTK+" vs. "GTK+ Python Bindings" - can this be made the same?



#: ../pitivi/discoverer.py:290
msgid "PiTiVi does not currently does not handle redirection files."

That's not a valid sentence.



#: ../pitivi/discoverer.py:302
msgid "An internal error occured while analyzing this file : %s"
#: ../pitivi/discoverer.py:407
msgid "Got unknown stream type : %s"
#: ../pitivi/ui/cam_capture.glade.h:1
msgid "Audio Capture Device :"
#: ../pitivi/ui/cam_capture.glade.h:4
msgid "Video Capture Device :"
#: ../pitivi/ui/encodingdialog.glade.h:1
msgid "<b>Audio :</b>"
#: ../pitivi/ui/encodingdialog.glade.h:4
msgid "<b>Video :</b>"
#: ../pitivi/ui/net_capture.glade.h:7
msgid "Customize :"
#: ../pitivi/ui/pluginmanagerdialog.py:271
msgid "Are you sure you want to remove selected plugins ?"
#: ../pitivi/ui/pluginmanagerdialog.py:321
msgid "Update the existent plugin ?"
#: ../pitivi/settings.py:167
msgid ""
"\n"
"Audio :"
#: ../pitivi/settings.py:170
msgid ""
"\n"
"Muxer :"

whitespace in front of a : or ? - not valid in non-french. ;-)



#: ../pitivi/pitivi.py:104
msgid "There is already a %s instance, inform developers"

Could be more polite, and could also tell *how* to inform developers.



#: ../pitivi/ui/cam_capture.glade.h:5
msgid "gtk-close"
#: ../pitivi/ui/cam_capture.glade.h:6
msgid "gtk-media-record"

Please set translatable to "no" here.



#: ../pitivi/ui/mainwindow.py:179
msgid "_Import from Webcam.."
#: ../pitivi/ui/mainwindow.py:182
msgid "_Make screencast.."
#: ../pitivi/ui/mainwindow.py:185
msgid "_Capture Network Stream.."

Should these be three dots instead?



#: ../pitivi/ui/net_capture.glade.h:2
msgid "Address "
#: ../pitivi/ui/net_capture.glade.h:9
msgid "Port "

Please remove the whitespace at the end of the string.



#: ../pitivi/ui/filelisterrordialog.py:75
msgid "URI : "
#: ../pitivi/ui/filelisterrordialog.py:81
msgid "Problem : "
#: ../pitivi/ui/filelisterrordialog.py:88
msgid "Extra information : "
#: ../pitivi/ui/gstwidget.py:175
msgid "Properties for "
#: ../pitivi/ui/net_capture.glade.h:1
msgid " Protocol"
#: ../pitivi/ui/pluginmanagerdialog.glade.h:3
msgid "Search : "
#: ../pitivi/ui/pluginmanagerdialog.glade.h:4
msgid "Show : "

Please remove any leading/ending whitespaces and whitespace in front of ":".
*If* you are concatenating stuff here then it's even worse and needs a proper fixing.
Especially "Properties for " looks very suspicious and breaks proper translation. Should probably be "Properties for %s".
See http://live.gnome.org/TranslationProject/DevGuidelines/Never%20split%20sentences .



#: ../pitivi/objectfactory.py:188
msgid "<b>%s</b><small>"
msgstr "<b>%s</b><small>"
#: ../pitivi/objectfactory.py:192
msgid "<b>%s</b> (%s)"
msgstr "<b>%s</b> (%s)"
#: ../pitivi/objectfactory.py:195
msgid "<b>%s</b>"
msgstr "<b>%s</b>"
#: ../pitivi/objectfactory.py:196
msgid "<small><b>File:</b> %s"
msgstr "<small><b>Datei:</b> %s"
#: ../pitivi/stream.py:185 ../pitivi/stream.py:255
msgid " <i>(%s)</i>"

That looks a bit error-prone.
E.g. "<b>%s</b> (%s)" cannot be properly localized without knowing what the strings stand for. See http://live.gnome.org/TranslationProject/DevGuidelines/Use%20comments .
msgid "<b>%s</b><small>" - so what if a translator removes the <small> by accident? This current string just looks very wrong to me.