Hello,

After updating Moodle 3.7.1, language customisation causing the "Error writing to database", preventing the language from loading for customization. MariaDB (5.6.45) was used: 

This is the debbuging report:

Debug info: Duplicate entry 'en-443-numberingstyleABC' for key 'mdl_toolcust_lancomstr_uix'
INSERT INTO mdl_tool_customlang (lang,componentid,stringid,original,master,timemodified,outdated,local,timecustomized) VALUES(?,?,?,?,?,?,?,?,?)
[array (
0 => 'en',
1 => '443',
2 => 'numberingstyleABC',
3 => 'A., B., C., ...',
4 => 'A., B., C., ...',
5 => 1563885209,
6 => 0,
7 => NULL,
8 => NULL,
)]
Error code: dmlwriteexception

Stack trace:

• line 489 of /lib/dml/moodle_database.php: dml_write_exception thrown
• line 1329 of /lib/dml/mysqli_native_moodle_database.php: call to moodle_database->query_end()
• line 1375 of /lib/dml/mysqli_native_moodle_database.php: call to mysqli_native_moodle_database->insert_record_raw()
• line 191 of /admin/tool/customlang/locallib.php: call to mysqli_native_moodle_database->insert_record()
• line 60 of /admin/tool/customlang/index.php: call to tool_customlang_utils::checkout()