Backdrop CMS does not support the default front page setting to be multilingual (one node for each language). Drupal 7 core does not either, but the contrib module i18n does. This feature would be helpful for Backdrop adoption in multilingual environments
However, there's a small workaround, using the redirect function in node settings. Just add a redirection to the default front page, pointing to the intended 2nd language front page node, and make this redirection language aware (2nd language).
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Worth mentioning as it was in zulip chat by @yorkshirepudding I just tested and the two work together without issue as long as you don't use the "Exclude comments from Content...
Search does not include comments
There is also Node Comments Search - this searches the node and all comments (default search is node and first page of comments) as part of the content search. Izzy's module above is a separate...
Search does not include comments
I have created a new module comment_search
Search does not include comments