Try dropping the first word, "Show".
$ grep -r "preview in image window" .
./plug-ins/jpeg/jpeg-save.c: gtk_check_button_new_with_mnemonic (_("Show _preview in image window"));
Binary file ./po-plug-ins/zh_CN.gmo matches
./po-plug-ins/pl.po:msgid "Show _preview in image window"
./po-plug-ins/ru.po:msgid "Show _preview in image window"
./po-plug-ins/nn.po:msgid "Show _preview in image window"
Binary file ./po-plug-ins/es.gmo matches
Binary file ./po-plug-ins/eu.gmo matches
./po-plug-ins/pt_BR.po:msgid "Show _preview in image window"
./po-plug-ins/ne.po:msgid "Show _preview in image window"
./po-plug-ins/gl.po:msgid "Show _preview in image window"
./po-plug-ins/sl.po:msgid "Show _preview in image window"
Binary file ./po-plug-ins/ne.gmo matches
./po-plug-ins/be.po:msgid "Show _preview in image window"
Binary file ./po-plug-ins/fr.gmo matches
./po-plug-ins/eo.po:msgid "Show _preview in image window"
./po-plug-ins/fa.po:msgid "Show _preview in image window"
Binary file ./po-plug-ins/pl.gmo matches
./po-plug-ins/cs.po:msgid "Show _preview in image window"
Binary file ./po-plug-ins/bg.gmo matches
./po-plug-ins/fr.po:msgid "Show _preview in image window"
./po-plug-ins/mk.po:msgid "Show _preview in image window"
./po-plug-ins/en_CA.po:msgid "Show _preview in image window"
./po-plug-ins/en_CA.po:msgstr "Show _preview in image window"
Binary file ./po-plug-ins/mk.gmo matches
Binary file ./po-plug-ins/uk.gmo matches
Binary file ./po-plug-ins/ca.gmo matches
./po-plug-ins/uk.po:msgid "Show _preview in image window"
./po-plug-ins/ja.po:msgid "Show _preview in image window"
./po-plug-ins/en_GB.po:msgid "Show _preview in image window"
./po-plug-ins/en_GB.po:msgstr "Show _preview in image window"
./po-plug-ins/ro.po:msgid "Show _preview in image window"
./po-plug-ins/et.po:msgid "Show _preview in image window"
./po-plug-ins/ca@valencia.po:msgid "Show _preview in image window"
./po-plug-ins/hu.po:msgid "Show _preview in image window"
./po-plug-ins/de.po:msgid "Show _preview in image window"
./po-plug-ins/km.po:msgid "Show _preview in image window"
Binary file ./po-plug-ins/gl.gmo matches
./po-plug-ins/zh_CN.po:msgid "Show _preview in image window"
Binary file ./po-plug-ins/pa.gmo matches
Binary file ./po-plug-ins/ru.gmo matches
./po-plug-ins/pa.po:msgid "Show _preview in image window"
Binary file ./po-plug-ins/et.gmo matches
Binary file ./po-plug-ins/sv.gmo matches
./po-plug-ins/bg.po:msgid "Show _preview in image window"
Binary file ./po-plug-ins/sk.gmo matches
./po-plug-ins/es.po:msgid "Show _preview in image window"
Binary file ./po-plug-ins/fi.gmo matches
./po-plug-ins/nl.po:msgid "Show _preview in image window"
./po-plug-ins/tt.po:msgid "Show _preview in image window"
./po-plug-ins/sk.po:msgid "Show _preview in image window"
Binary file ./po-plug-ins/hu.gmo matches
./po-plug-ins/it.po:msgid "Show _preview in image window"
./po-plug-ins/gu.po:msgid "Show _preview in image window"
Binary file ./po-plug-ins/pt_BR.gmo matches
./po-plug-ins/dz.po:msgid "Show _preview in image window"
Binary file ./po-plug-ins/sl.gmo matches
Binary file ./po-plug-ins/km.gmo matches
Binary file ./po-plug-ins/dz.gmo matches
Binary file ./po-plug-ins/it.gmo matches
./po-plug-ins/ar.po:msgid "Show _preview in image window"
Binary file ./po-plug-ins/gu.gmo matches
Binary file ./po-plug-ins/ar.gmo matches
Binary file ./po-plug-ins/lt.gmo matches
./po-plug-ins/ko.po:msgid "Show _preview in image window"
Binary file ./po-plug-ins/en_CA.gmo matches
./po-plug-ins/fi.po:msgid "Show _preview in image window"
Binary file ./po-plug-ins/ja.gmo matches
Binary file ./po-plug-ins/cs.gmo matches
./po-plug-ins/sv.po:msgid "Show _preview in image window"
./po-plug-ins/ca.po:msgid "Show _preview in image window"
Binary file ./po-plug-ins/de.gmo matches
Binary file ./po-plug-ins/vi.gmo matches
./po-plug-ins/oc.po:msgid "Show _preview in image window"
./po-plug-ins/vi.po:msgid "Show _preview in image window"
./po-plug-ins/lt.po:msgid "Show _preview in image window"
./po-plug-ins/eu.po:msgid "Show _preview in image window"
Binary file ./po-plug-ins/en_GB.gmo matches
$