No, that is worse than {{SITENAME}}. Read https://www.mediawiki.org/wiki/Localisation#Avoid_.7B.7BSITENAME.7D.7D_in_messages

If questions remain, ask them. Maybe the above section is too terse.

In T122788#1924587, @Jdforrester-WMF wrote:

The alternative is making translators write each of the thousands of messages. This situation is acceptable, IMO.

This is nonsense, not an alternative. Please read https://www.mediawiki.org/wiki/Localisation#Avoid_.7B.7BSITENAME.7D.7D_in_messages
There is no need for more than one message and there is no necessity for {{SITENAME}} here.

Please tell, if https://www.mediawiki.org/wiki/Localisation#Avoid_.7B.7BSITENAME.7D.7D_in_messages is not clear enough and needs better wording.

It's entirely "clear". It's just not something we agree with.