Hreflang annotation is supported by Google and Yandex to allow your site to communicate with the search engines which country and language the content is intended for.
Google started notifying incorrect hreflang tags implementation in its search console which signifies the importance of implementing the annotation correctly.
On the other hand, according to this seroundtable.com post, Google will simply ignore the incorrectly implemented hreflang tags rather than penalise it.
This is a good news for many of us since hreflang tags need to be implemented at page level and a cluster (i.e. the tags need to be implemented on all the corresponding international pages, not just one country) so it requires substantial resource to get the tags implemented right the first time round.
Currently there isn’t a good Free WordPress plugin solution for implementing hreflang tags but if you don’t mind spending a bit of money, https://wpml.org/ offers a paid “WordPress Multilingual Plugin” that can let you insert the hreflang tags on your site.
Since we have not tested the Plugin it is difficult to say how easily hreflang tags can be added but according to this support forum post from their site, the plugin for sure provides the function to add hreflang tags.