fix: monkey patch the @translation GET endpoint avoiding a useless search if plone.app.multilingual is not installed

[luca-bellenghi]

missing compatibility with Plone5.2

[coveralls]

Pull Request Test Coverage Report for Build 6313279862

• 2 of 5 (40.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.1%) to 62.85%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/redturtle/volto/monkey.py	2	5	40.0%
<!--	Total:	2	5	40.0%	-->

Totals
Change from base Build 6311070427:	-0.1%
Covered Lines:	763
Relevant Lines:	1214

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💛 - Coveralls