[sv-SE] Update sv-SE, added Language.PHP and missing HTTP strings

[tangix]

Description Supersedes #424

Another try at the PR from yesterday... Updated sv_SE language with Language.php and missing JSON related strings in HTTP.php

Checklist:

• [X] Securely signed commits
• [ ] Component(s) with PHPDoc blocks, only if necessary or adds value
• [ ] Unit testing, with >80% coverage
• [ ] User guide updated
• [X] Conforms to style guide