Replace manual activerecord translations with helpers

config/locales/en/exercise.yml

@@ -7,11 +7,11 @@ en:
         allow_file_creation: Allow file creation
         average_score_percentage: Average Score Percentage
         description: Description
-        difficulty: Difficulty
         distinct_final_submissions: Distinct Final Submissions
         embedding_parameters: LTI Embedding Parameters
         execution_environment: Execution Environment
         execution_environment_id: Execution Environment
+        expected_difficulty: Difficulty
         files: Files
         finishing_rate: Finishing Rate
         hide_file_tree: Hide File Tree

config/locales/en/exercise_collection.yml

@@ -2,7 +2,7 @@
 en:
   activerecord:
     attributes:
-      exercise_collections:
+      exercise_collection:
         exercises: Exercises
         id: ID
         name: Name

config/locales/en/meta/activerecord.errors.yml

@@ -4,12 +4,15 @@ en:
     errors:
       messages:
         at_least: or %{attribute} must be defined
-        together: has to be set along with %{attribute}
+        together: must be defined along with %{attribute}
       models:
         exercise:
-          at_most_one_main_file: must include at most one main file
-          late_submission_deadline_not_alone: must not be used without a regular submission deadline
-          late_submission_deadline_not_before_submission_deadline: must not be before the submission deadline passed
+          attributes:
+            files:
+              at_most_one_main_file: must include at most one main file
+            late_submission_deadline:
+              not_alone: must not be used without a regular submission deadline
+              not_before_submission_deadline: must not be before the submission deadline passed
         internal_user:
           attributes:
             password:

config/locales/en/request_for_comment.yml

@@ -2,7 +2,7 @@
 en:
   activerecord:
     attributes:
-      request_for_comments:
+      request_for_comment:
         close: Close window
         comments: Comments
         execution_environment: Language

config/locales/en/tip.yml

@@ -5,6 +5,7 @@ en:
       tip:
         description: Description
         example: Example
+        file_type: File Type
         title: Title
     models:
       tip: