Launchpad currently recommends translating gtk+3.0 in Ubuntu Cosmic.

Template "gtk-3.0" in Ubuntu Cosmic package "gtk+3.0"

Language Status Untranslated Need review Changed Last Edited By
Cherokee 100.00  100.0% untranslated 1663 1663 0 0
Dakota 100.00  100.0% untranslated 1663 1663 0 0
Hawaiian 100.00  100.0% untranslated 1663 1663 0 0
Inuktitut 100.00  100.0% untranslated 1663 1663 0 0
Lakota 100.00  100.0% untranslated 1663 1663 0 0
Ojibwe 100.00  100.0% untranslated 1663 1663 0 0
Spanish 000.00  100.0% translated 0 0 18 18 2019-02-10 09:44:16 UTC 2019-02-10 Daniel Mustieles
Tlingit 100.00  100.0% untranslated 1663 1663 0 0
Yiddish 097.78  2.22489476849% translated  97.7751052315% untranslated 1626 1626 0 0 2019-02-10 10:09:52 UTC 2019-02-10 Raphael Finkel
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Template "gtk-3.0-properties" in Ubuntu Cosmic package "gtk+3.0"

Language Status Untranslated Need review Changed Last Edited By
Cherokee 100.00  100.0% untranslated 2243 2243 0 0
Dakota 100.00  100.0% untranslated 2243 2243 0 0
Hawaiian 100.00  100.0% untranslated 2243 2243 0 0
Inuktitut 100.00  100.0% untranslated 2243 2243 0 0
Lakota 100.00  100.0% untranslated 2243 2243 0 0
Ojibwe 100.00  100.0% untranslated 2243 2243 0 0
Spanish 000.00  100.0% translated 0 0 28 28 2019-02-10 10:11:37 UTC 2019-02-10 Daniel Mustieles
Tlingit 100.00  100.0% untranslated 2243 2243 0 0
Yiddish 070.80  29.2019616585% translated  70.7980383415% untranslated 1588 1588 0 0 2019-02-10 10:31:56 UTC 2019-02-10 Raphael Finkel
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Key to this table: “Unchanged” means Translated
and “untranslated” means just that, Untranslated

Other versions of gtk+3.0 in Ubuntu