Add welsh translations

Author: TawneeOwl

app/translations/cy/LC_MESSAGES/messages.po

@@ -465,10 +465,10 @@ msgid "None of these"
 msgstr "Dim un o'r rhain"
 
 msgid "Is this to do with police, prisons or detention centres?"
-msgstr ""
+msgstr "A yw hyn yn ymwneud â’r heddlu, carchardai neu ganolfannau cadw?"
 
 msgid "Select if this is about the police, prisons or detention centres"
-msgstr ""
+msgstr "Dewiswch a yw hyn yn ymwneud â’r heddlu, carchardai neu ganolfannau cadw"
 
 msgid "Are you under 18?"
 msgstr "Ydych chi dan 18 oed?"
@@ -1713,7 +1713,7 @@ msgid "Email"
 msgstr "E-bost"
 
 msgid "Legal action against public organisations"
-msgstr ""
+msgstr "Camau cyfreithiol yn erbyn sefydliadau cyhoeddus"
 
 msgid ""
 "Legal help to challenge something done by a public organisation. You "