Fix i18n messages, back to 16 supported shape #13162

Job	Run time
Core Basic (14.x)	7m 49s
Core Basic - Plone 5 (16.x)	8m 28s
Core Blocks (14.x)	10m 46s
Core Basic (16.x)	8m 1s
Core Blocks (16.x)	10m 10s
Core Basic (18.x)	7m 42s
Coresandbox (16.x, 3.7)	5m 1s
Core Blocks (18.x)	11m 13s
Core Volto Slate (14.x)	8m 26s
Core Volto Slate (16.x)	8m 16s
Guillotina (16.x)	4m 4s
Project Generator (16.x)	4m 34s
Core Volto Slate (18.x)	8m 34s
Multilingual (16.x)	3m 38s
Project Generator (18.x)	4m 27s
Multilingual in Seamless Mode (18.x)	3m 52s
Seamless Mode (16.x)	8m 2s
Working Copy (16.x)	3m 38s
	2h 6m 41s

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