Convert the 'translation_language_type' variable to CMI

the translation_ prefix can be removed, that is no longer necessary. Looks good otherwise.

+++ b/core/modules/translation/config/translation.settings.ymlundefined
@@ -0,0 +1 @@
+language_type: "language_interface"
\ No newline at end of file

+++ b/core/modules/translation/translation.installundefined
@@ -15,3 +15,16 @@ function translation_update_8000() {
+}
\ No newline at end of file

Make sure to add an empty line at the end of these two files so that git stops complaining about it.

+++ b/core/modules/translation/translation.installundefined
@@ -15,3 +15,16 @@ function translation_update_8000() {
     ->execute();
 }
+
+
+/**
+* Moves "translation_language_type" from variable to config.

While you're at it, there is one empty line too much here, that's not necessary.

Looks good, RTBC if the tests pass.

RTBCing.

Committed/pushed to 8.x, thanks!