[i18n] Enable Latvian translation (#9079)

Cf. <https://github.com/koreader/koreader/issues/8225#issuecomment-1120181554>.

frontend/gettext.lua

@@ -216,6 +216,11 @@ function GetText_mt.__index.changeLang(new_lang)
                     if plurals == "n == 1) ? 0 : ((n == 2) ? 1 : ((n > 10 && n % 10 == 0) ? 2 : 3)" then
                         plurals = "n == 1 ? 0 : (n == 2) ? 1 : (n > 10 && n % 10 == 0) ? 2 : 3"
                     end
+                    -- Hardcoded workaround for Latvian.
+                    print(plurals)
+                    if plurals == "n % 10 == 0 || n % 100 >= 11 && n % 100 <= 19) ? 0 : ((n % 10 == 1 && n % 100 != 11) ? 1 : 2" then
+                        plurals = "n % 10 == 0 || n % 100 >= 11 && n % 100 <= 19 ? 0 : (n % 10 == 1 && n % 100 != 11) ? 1 : 2"
+                    end
                     -- Hardcoded workaround for Romanian which has 3 plural forms.
                     if plurals == "n == 1) ? 0 : ((n == 0 || n != 1 && n % 100 >= 1 && n % 100 <= 19) ? 1 : 2" then
                         plurals = "n == 1 ? 0 : (n == 0 || n != 1 && n % 100 >= 1 && n % 100 <= 19) ? 1 : 2"

frontend/ui/language.lua

@@ -18,6 +18,7 @@ local Language = {
         he = "עִבְרִית",
         hu = "Magyar",
         ka = "ქართული",
+        lv = "Latviešu",
         nl_NL = "Nederlands",
         nb_NO = "Norsk",
         pl = "Polski",
@@ -124,6 +125,7 @@ function Language:getLangMenuTable()
                 self:genLanguageSubItem("gl"),
                 self:genLanguageSubItem("it_IT"),
                 self:genLanguageSubItem("hu"),
+                self:genLanguageSubItem("lv"),
                 self:genLanguageSubItem("nl_NL"),
                 self:genLanguageSubItem("nb_NO"),
                 self:genLanguageSubItem("pl"),