Prerequisites 

• One page tree per country ("country branch")
• Root of each country branch has the option "Use as Root Page" set
• Crosslinks between the country branches work. Perhaps you have to set config.typolinkCheckRootline = 1 and config.typolinkEnableLinksAcrossDomains = 1 in your TypoScript setup.
• If you have MountPages, try to set config.MP_disableTypolinkClosestMPvalue = 1 in your TypoScript setup.
• If you activated the EXT:seo (typo3/cms-seo), you should disable it's hreflang generation
• • in TYPO3 9.5LTS with unset($GLOBALS['TYPO3_CONF_VARS']['SC_OPTIONS']['TYPO3\CMS\Frontend\Page\PageGenerator']['generateMetaTags']['hreflang']); in the AdditionalConfiguration.php or your Theme-Extension's ext_localconf.php
• • in TYPO3 10.4LTS by not setting hreflang in your site config languages (or wait for EXT:bgm_hreflang version 5 :-))

Since version 4.0 you have to use the new page translation without the table "pages_language_overlay"!