Apply coding standards

After the patch #2 module still needs work on the following files (checked with Drupal and DrupalPractice standards):

/languagefield.info.yml
/src/Controller/LanguageAutocompleteController.php
/src/CustomLanguageListBuilder.php
/src/Entity/CustomLanguage.php
/src/Entity/CustomLanguageInterface.php
/src/Entity/CustomLanguageManager.php
/src/Form/CustomLanguageForm.php
/src/Plugin/Field/FieldFormatter/LanguageFormatter.php
/src/Plugin/Field/FieldType/LanguageItem.php
/src/Plugin/Field/FieldWidget/LanguageAutocompleteWidget.php
/src/Plugin/Field/FieldWidget/LanguageSelectWidget.php
/src/Plugin/views/filter/LanguageFilter.php

This is true for the module:
version: '8.x-1.4'
core: '8.x'

Ok, I see. In that case the patch fixed given files according to coding standards.

For further improvements see comment #5.

Committed. Thanks. Back to active for more files.

Sorry wrong edit.

Committed, thanks.
Only the following parts have not been changed, since it changes behaviour without justification:

-            $subsettable_languages[$langcode] = t($language_names[0]);
+            $subsettable_languages[$langcode] = $language_names[0];

         LanguageInterface::LANGCODE_NOT_SPECIFIED => $this->t('Language neutral'),
-        'current_interface' => $this->t('Current interface language') . '*',
-        'authors_default' => $this->t("Author's preferred language") . '*',
+        'current_interface' => $this->t('Current interface language'),
+        'authors_default' => $this->t("Author's preferred language"),

       switch ($format) {
         case 'en':
-          $language_name .= $this->t($language_names[0]);
+          $language_name .= $language_names[0];
           break;

Translating Variables

You should never use t() to translate variables, such as calling

t($text);

, unless the text that the variable holds has been passed through t() elsewhere (e.g., $text is one of several translated literal strings in an array). It is especially important never to call

t($user_text);

, where $user_text is some text that a user entered - doing that can lead to cross-site scripting and other security problems. However, you can use variable substitution in your string, to put variable text such as user names or link URLs into translated text. Variable substitution looks like this:

$text = t("@name's blog", array(
  '@name' => format_username($account),
));

@from https://api.drupal.org/api/drupal/includes%21bootstrap.inc/function/t/7.x

Hi!
The following change in getLanguageConfigurationValues caused an issue:
- $value = $code;
+ $value = LanguageInterface::LANGCODE_NOT_SPECIFIED;

Its fixed at #3125977: Widget 'Language select list' does not save selected value