Upgrading from 4.2.1 to 5.4.2, before upgrading to 5.4.3 due to GDPR compliance

[gamevilcom2us]

I'm trying to upgrade my forum v4.2.1 to v5.4.2 and following upgrad instruction.

Once open update.php, I put my customer number then start upgrade then message appeared like below:

Action Required
Unexpected Text:
The requested language does not exist, reset via tools.php.
Script: 422a1
Step: 1

so I put tools.php in the ./core/install folder and open tools.php and clicked [Language] link.
but It is not fixed.

How can I solve this issue?


My current server setting is below:
+----------------------------
| ubuntu 14.04
| Apache/2.4.7 (Ubuntu)
| PHP 7.1.19-1+ubuntu14.04.1+deb.sury.org+1
| MySQL Ver 14.14 Distrib 5.5.60
+----------------------------