By default without adding any wpml-config.xml file, wordpress seo strings show up at admin polylang settings to enter each language translation. It turns that it doesn't work.
But if you add them at wpml-config.xml it works.
As a result these Yoast wp-option fields show up at polylang settings twice. The originals, the ones from the plugin integration with Yoast are in wordpress seo group, the ones added at wpml-config.xml file show up at theme's group. These mentioned groups show up at first column of the table of the admin polylang settings.
All I had to do was leave alone the wordpress seo group and set my meta titles translation at theme group.
Here's my wpml-config.xml file saved at child theme folder:
<wpml-config>
<admin-texts>
<key name="wp_cart_title" />
<key name="wp_cart_empty_text" />
<key name="addToCartButtonName" />
<key name="cart_return_from_paypal_url" />
<key name="cart_products_page_url" />
<key name="cart_checkout_page_url" />
<key name="pitch_theme_settings">
<key name="front_page_portfolio_home" />
<key name="front_page_cta_text" />
<key name="front_page_cta_button_text" />
<key name="front_page_cta_button_url" />
<key name="front_page_home_blog" />
<key name="front_page_home_title_latest_projects" />
<key name="front_page_home_title_blog" />
<key name="front_page_home_title_clients" />
<key name="project_tags" />
<key name="project_archive_title" />
<key name="project_view_text" />
<key name="project_url_slug" />
<key name="type_project" />
<key name="type_feature" />
<key name="type_client" />
<key name="type_slide" />
<key name="text_footer_text" />
<key name="text_search_placeholder" />
<key name="text_comments_closed" />
<key name="text_not_found" />
<key name="general_demo_mode" />
<key name="general_search_input" />
<key name="general_menu_extras" />
<key name="general_topbar_menu" />
<key name="general_scale_main_menu" />
</key>
<key name="wpseo_titles">
<key name="title-skill" />
<key name="title-category" />
<key name="title-post_tag" />
<key name="title-author" />
<key name="title-archive" />
<key name="title-search" />
<key name="title-404" />
<key name="title-ptarchive-project" />
</key>
</admin-texts>
</wpml-config>