core&ui: problem_main: support sort

packages/ui-default/locales/en.yaml

@@ -27,9 +27,9 @@ problem_import: Import Problem
 problem_main: Problem Set
 problem_solution: Problem Solution
 problem_submit: Problem Submit
+problem_type.communication: 'Type: Communication'
 problem_type.default: 'Type: Default'
 problem_type.interactive: 'Type: Interactive'
-problem_type.communication: 'Type: Communication'
 problem_type.objective: 'Type: Objective'
 problem_type.remote_judge: 'Type: RemoteJudge'
 problem_type.submit_answer: 'Type: SubmitAnswer'
@@ -54,6 +54,8 @@ setting_info: Personal Info
 setting_preference: Preference
 setting_privacy: Privacy
 setting_usage: Usage Preference
+sort::default: Default
+sort::recent: Recent
 tasks_list: Task list
 timeago_locale: en_US
 training_create: Training Create