If you can supply the image url in source tag for renditions, HTML + Browser will do rest of the work for youRefer: https://webdesign.tutsplus.com/tutorials/quick-tip-how-to-use-html5-picture-for-responsive-images--cms-21015

It highly varies from project, users and  a lot of factors...Must look at https://helpx.adobe.com/experience-manager/6-2/managing/using/hardware-sizing-guidelines.html#Publishenvironmentspecificcalculations

Typically a sitemap is updated after 12hr or 24hr via a scheduled job which takes care of iterating JCR structure once and caching it in dispatcher till next version of sitemap gets generated by job.Making changes in existing file might created overhead if these changes are large number also, I am n...

Your understanding is correct, it picks the osgi config in front of publish.Can you share your externalizer configs?

There is no simple answer to your question like 2, 4, 8 GB ram would be enough.You would definitely want to enough RAM in Author instance machine so that it does not affect the productivityWhen it comes to author sizing guidelines, a lot of factors needs to be considered like below but not limited t...

Are you using workflow to create the page?I skeptical if you can return the response from workflow to browser via sling servlet

In order to retrieve value you can use any of these${currentPage.language.toString}${currentPage.language.language}Just in case you need API references-https://helpx.adobe.com/experience-manager/6-3/sites/developing/using/reference-materials/javadoc/com/day/cq/wcm/api/Page.html#getLanguage()

Similar issue was also reported for 6.3 as well.Make sure you do not have any space in path to jar file else it will through an crypto exception in stderr.logReferences from Windows OSPath with spaces - C:\AEM Stuff\aem 6.4 - will not workPath without spaces - C:\sample\aem64 - will work

1 .Make you have proper configs in editconfig https://helpx.adobe.com/experience-manager/6-3/sites/developing/using/components-basics.html 2. Someone would have added custom action which might be causing the issueand if its even happening with OOTB components, share component name and steps to repro...

For siteadmin action files in classic ui, you can refer to /libs/cq/ui/widgets/source/widgets/wcm/libs/cq/ui/widgets/source/widgets/wcm/SiteAdmin.Actions.js