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 1665 1665 0 0
Dakota 100.00  100.0% untranslated 1665 1665 0 0
Hawaiian 100.00  100.0% untranslated 1665 1665 0 0
Inuktitut 100.00  100.0% untranslated 1665 1665 0 0
Lakota 100.00  100.0% untranslated 1665 1665 0 0
Ojibwe 100.00  100.0% untranslated 1665 1665 0 0
Spanish 000.72  99.2792792793% translated  0.720720720721% untranslated 12 12 0 20 20 2018-08-11 14:05:24 UTC 2018-08-11 Rodrigo
Tlingit 100.00  100.0% untranslated 1665 1665 0 0
Yiddish 097.78  2.22222222222% translated  97.7777777778% untranslated 1628 1628 0 0 2018-07-22 13:31:38 UTC 2018-07-22 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 2241 2241 0 0
Dakota 100.00  100.0% untranslated 2241 2241 0 0
Hawaiian 100.00  100.0% untranslated 2241 2241 0 0
Inuktitut 100.00  100.0% untranslated 2241 2241 0 0
Lakota 100.00  100.0% untranslated 2241 2241 0 0
Ojibwe 100.00  100.0% untranslated 2241 2241 0 0
Spanish 000.00  100.0% translated 0 0 28 28 2018-08-11 16:53:55 UTC 2018-08-11 Rodrigo
Tlingit 100.00  100.0% untranslated 2241 2241 0 0
Yiddish 070.77  29.2280232039% translated  70.7719767961% untranslated 1586 1586 0 0 2018-07-22 13:09:07 UTC 2018-07-22 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