How to get language independent ACF theme options on a WPML site

language-independent-acf-theme-options-output.php

<?php
/**
 * To get this to work, you need to tinker with the acf/settings/ filter and reset the default language
 * so that the get_field() function returns the correct results even when not on the default language.
 * 
 * You can add the filter before you call the get_field() function and then call it again with the current 
 * language to reset it again, so it will affect other pages.
 * 
 * answer courtesy of James of ACF Support
 */

// add this
add_filter( 'acf/settings/current_language', function() {
     global $sitepress;
     return $sitepress->get_default_language();
});

// this is already in your code
$my_field =  get_field( 'my_field', 'option' );

// reset to original language
add_filter( 'acf/settings/current_language', function() {
     return ICL_LANGUAGE_CODE;
});

This was extremely helpful! thanks!

Hi and thanks for the code-snippets.

Because there is no way to handle this smart in the WP-Backend (see the comment of @elliottmangham) I use the "language=all"-soloution with a force-redirect in the backend by admin_init-action.

Template-Code:

// Use this to force ACF to look for the "all" version of the fields.
	add_filter('acf/settings/current_language', function() { return 'all' ; } );

// Insert your regular ACF code between the add_filter and remove_filter lines.
	echo get_field('my_language_independet_option_field', 'option');

// Use this to re-enable language-specific retrieval of ACF fields.
	remove_filter('acf/settings/current_language', function() { return ICL_LANGUAGE_CODE ; } );

Backend- / Admin-Code (functions.php):

function force_redirect_to_the__all__version_of_global_options() {
	// correct page
		global $pagenow ;
		if($pagenow === "admin.php" && isset($_GET['page']) && $_GET['page'] === "global-options") { // global-options is the menu_slug you defined in acf_add_options_page
			// lang not 'all'?
				if(ICL_LANGUAGE_CODE !== 'all') {
					// manipulate query (set lang to "all")
						$query = $_GET;
						$query['lang'] = 'all';
						$query_result = http_build_query($query);
					// redirect and die
						wp_redirect(get_admin_url() . 'admin.php?' . $query_result);
						die();
				}
		}
}
add_action( 'admin_init', 'force_redirect_to_the__all__version_of_global_options');

Nice gist, in particular the solution by @peterblickenstorfer (Backend/Admin Code) works for me. I just needed to group the really global option fields to a separate field group and option page.

It does makes a lot of sense to use the "All Languages" instead of setting the default language custom fields.

Update:
I have posted too soon without checking if things are working properly. There is just something wrong when I used add_filter('acf/settings/current_language', function() { return 'all' ; } );. It might be my WPML setup?

So I have reverted back to using the "default language" field as a global field, and used the Backend/Admin Code by @peterblickenstorfer