Background of the issue:
We would like to replace a single word sitewide: aluminium to aluminum. It's in the original English but also many translations. Possible also in some slugs. We fear that if we use something like Better Search & Replace it will at least make WPML forget some of the previously translated texts. Or, at worst, forget many texts and potentially break translations and pages.
Symptoms:
We fear that using a search and replace tool might make WPML forget some of the previously translated texts or break translations and pages.
Questions:
Is there a best practice to do a simple search & replace sitewide?
I don't know any best practices for using search and replace sitewide. I suggest you take a backup of your site and try it. Or better yet, try it on a copy of your site before you try it on the production site. This matter is out of the scope of our support forum. If the word "aluminium" also shows in the translations, then, to the best of my knowledge, it should also be replaced in the translation. Then, in my opinion, if you don't "touch" the wp_icl_ tables (WPML's DB tables), there should be no problem with breaking or losing the translations. I've never tried such a thing. Please do you experiments with that.
**** Important! Please make a full site backup (files and DB) before you proceed with those steps****
However, please know that WPML's Advanced Translation Editor has a great feature called "Glossary". WPML’s glossary lets you create better translations by defining how you want certain words to appear in your site’s translations. You can read about it here.
The glossary is not a solution for what you are trying to achieve. However, it is a solution for keeping the word "aluminium" the same in the translations.