My site has the same bug like this: http://www.question2answer.org/qa/11447/1-5-beta-bug-no-selected-class-for-extra-links-in-page-menu
But I can't update my site to V1.5.1 or V1.5.2 since I have done many changes.I know the newest version has fixed it, how can I fix it in version V1.5?
One way would be to check the diffs on Github: https://github.com/q2a/question2answer/commits/ the code changes will be in there somewhere.
Alternatively, if you have marked all your custom changes (i.e. with a special comment) you can backup your Q2A, overwrite with the new version, then copy your changes back.
By the way, it's very likely that most of your changes could be made via plugins or an advanced theme.
I find the answer,update qa-page.php, like below:
foreach ($qa_content['navigation'] as $navtype => $navigation)
if (is_array($navigation) && ($navtype!='cat'))
foreach ($navigation as $navprefix => $navlink)
if ((substr($requestlower.'$', 0, strlen($navprefix)) == $navprefix)||(strtolower(@$navlink['url'])==$selfpathhtml))
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July 15, 2020: Q2A 1.8.5 released!