I have posted a possible solution on the forum.
I am not sure it would be B/C. @mbabker ?
Here is the .diff to test

diff --git a/modules/mod_languages/tmpl/default.php b/modules/mod_languages/tmpl/default.php
index 0192c3f..eb9c061 100644
--- a/modules/mod_languages/tmpl/default.php
+++ b/modules/mod_languages/tmpl/default.php
@@ -27,4 +27,5 @@
 	<select class="inputbox advancedSelect" onchange="document.location.replace(this.value);" >
 	<?php foreach ($list as $language) : ?>
+	<?php $language->link = rtrim($language->link, '/'); ?>
 		<option dir=<?php echo $language->rtl ? '"rtl"' : '"ltr"'; ?> value="<?php echo htmlspecialchars_decode(htmlspecialchars($language->link, ENT_QUOTES, 'UTF-8'), ENT_NOQUOTES); ?>" <?php echo $language->active ? 'selected="selected"' : ''; ?>>
 		<?php echo $language->title_native; ?></option>
@@ -35,4 +36,5 @@
 	<div class="btn-group">
 		<?php foreach ($list as $language) : ?>
+		<?php $language->link = rtrim($language->link, '/'); ?>
 			<?php if ($language->active) : ?>
 				<a href="#" data-toggle="dropdown" class="btn dropdown-toggle">
@@ -47,4 +49,5 @@
 		<ul class="<?php echo $params->get('lineheight', 0) ? 'lang-block' : 'lang-inline'; ?> dropdown-menu" dir="<?php echo JFactory::getLanguage()->isRtl() ? 'rtl' : 'ltr'; ?>">
 		<?php foreach ($list as $language) : ?>
+		<?php $language->link = rtrim($language->link, '/'); ?>
 			<?php if (!$language->active) : ?>
 				<li>
@@ -73,4 +76,5 @@
 	<ul class="<?php echo $params->get('inline', 1) ? 'lang-inline' : 'lang-block'; ?>" dir="<?php echo JFactory::getLanguage()->isRtl() ? 'rtl' : 'ltr'; ?>">
 	<?php foreach ($list as $language) : ?>
+		<?php $language->link = rtrim($language->link, '/'); ?>
 		<?php if (!$language->active) : ?>
 			<li>
diff --git a/plugins/system/languagefilter/languagefilter.php b/plugins/system/languagefilter/languagefilter.php
index 7ab830b..8d17606 100644
--- a/plugins/system/languagefilter/languagefilter.php
+++ b/plugins/system/languagefilter/languagefilter.php
@@ -228,5 +228,5 @@
 			|| $lang !== $this->current_lang))
 		{
-			$uri->setPath($uri->getPath() . '/' . $sef . '/');
+			$uri->setPath($uri->getPath() . '/' . $sef);
 		}
 	}
@@ -836,4 +836,5 @@
 				foreach ($languages as $i => &$language)
 				{
+					$language->link = rtrim($language->link, '/');
 					$doc->addHeadLink($server . $language->link, 'alternate', 'rel', array('hreflang' => $i));
 				}

btw, I do not have here a trailing slash for any menu items except home before this proposed patch.
But it could solve your issue if you get one.
The .diff proposed deals with menu items, language switcher and hreflang and is in my tests case specifically useful for Homes.

Hi, thanks for the quick reply!
For me also, all the normal links to articles don't have a trailing slash.
If I understand correctly, you strip the trailing slash off of any link. On one hand that seems very reliable because it would work on all links processed by this code. On the other hand, wouldn't it be better to not add the slash there in the first place? So far I've only seen it happen in the language plugin and blog type link. For consistency and efficiency I'd probably change those instead of repairing it afterwards.
Don't get me wrong though, I really appreciate your effort!

Willem

The way I see it, the trailing slash is specific to multilingual sites and even more specific to the Home pages of such sites where only the sef url language code is displayed after the domain or after TLD/index.php

Therefore this PR deals only with the multilingual module switcher and language filter plugin.

As I said, I can't reproduce the trailing slash for any other loaded page, including /blog but I guess the pr would solve your issue too. Please test.

any Comment @DeWillem78 or can this Issue be closed?

any Comment @DeWillem78 or can this Issue be closed?

Set to "closed" on behalf of @franz-wohlkoenig by The JTracker Application at issues.joomla.org/joomla-cms/23209

Closed as no Answer, please reopen if needed.