This sample shows how to automatically replace <textarea> elements with a CKEditor instance with an option to change the language of its user interface.

It pulls the language list from CKEditor _languages.js file that contains the list of supported languages and creates a drop-down list that lets the user change the UI language.

By default, CKEditor automatically localizes the editor to the language of the user. The UI language can be controlled with two configuration options: language and defaultLanguage. The defaultLanguage setting specifies the default CKEditor language to be used when a localization suitable for user's settings is not available.

To specify the user interface language that will be used no matter what language is specified in user's browser or operating system, set the language property:

CKEDITOR.replace( 'textarea_id', {
    // Load the German interface.
    language: 'de'
});

    <p>
        Note that <code><em>textarea_id</em></code> in the code above is the <code>id</code> attribute of
        the <code>&lt;textarea&gt;</code> element to be replaced.
    </p>
</div>
<form action="sample_posteddata.php" method="post">
    <p>
        Available languages (<span id="count"> </span> languages!):<br>
        <script>

            document.write( '<select disabled="disabled" id="languages" onchange="createEditor( this.value );">' );

            // Get the language list from the _languages.js file.
            for ( var i = 0 ; i < window.CKEDITOR_LANGS.length ; i++ ) {
                document.write(
                    '<option value="' + window.CKEDITOR_LANGS[i].code + '">' +
                        window.CKEDITOR_LANGS[i].name +
                    '</option>' );
            }

            document.write( '</select>' );

        </script>
        <br>
        <span style="color: #888888">
            (You may see strange characters if your system does not support the selected language)
        </span>
    </p>
    <p>
        <textarea cols="80" id="editor1" name="editor1" rows="10">&lt;p&gt;This is some &lt;strong&gt;sample text&lt;/strong&gt;. You are using &lt;a href="https://ckeditor.com/"&gt;CKEditor&lt;/a&gt;.&lt;/p&gt;</textarea>
        <script>

            // Set the number of languages.
            document.getElementById( 'count' ).innerHTML = window.CKEDITOR_LANGS.length;

            var editor;

            function createEditor( languageCode ) {
                if ( editor )
                    editor.destroy();

                // Replace the <textarea id="editor"> with an CKEditor
                // instance, using default configurations.
                editor = CKEDITOR.replace( 'editor1', {
                    language: languageCode,

                    on: {
                        instanceReady: function() {
                            // Wait for the editor to be ready to set
                            // the language combo.
                            var languages = document.getElementById( 'languages' );
                            languages.value = this.langCode;
                            languages.disabled = false;
                        }
                    }
                });
            }

            // At page startup, load the default language:
            createEditor( '' );

        </script>
    </p>
</form>
<div id="footer">
    <hr>
    <p>
        CKEditor - The text editor for the Internet - <a class="samples" href="https://ckeditor.com/">https://ckeditor.com</a>
    </p>
    <p id="copy">
        Copyright &copy; 2003-2019, <a class="samples" href="https://cksource.com/">CKSource</a> - Frederico
        Knabben. All rights reserved.
    </p>
</div>