Mark strings for translations #606

Job	Run time
testsuite / testsuite-linux (8.1, highest, false)	37s
cs-stan / Coding Standard & Static Analysis	41s
testsuite / testsuite-linux (8.3, highest, false)	36s
testsuite / testsuite-linux (8.4, highest, false)	1m 15s
testsuite / testsuite-linux (8.2, highest, false)	40s
testsuite / testsuite-linux (8.1, lowest, false)	31s
	4m 20s

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