ListPreference: refer item in string-array as defaultValue

Question

I use PreferenceFragmentCompat to generate setting ui.

Here is my simple setting

<PreferenceCategory app:title="@string/language_setting_header">
    <ListPreference
        app:defaultValue="en"
        app:entries="@array/language_entries"
        app:entryValues="@array/language_values"
        app:key="@string/key_lang"
        app:title="@string/language_setting_title"
        app:useSimpleSummaryProvider="true" />

</PreferenceCategory>

Here is my array

<resources>
<!-- Language Preference -->
<string-array name="language_entries">
    <item>English</item>
    <item>ภาษาไทย</item>
</string-array>

<string-array name="language_values">
    <item>en</item>
    <item>th</item>
</string-array>

I want to make thing consistency by

app:defaultValue="@array/language_values/en"

The Android Studio come with error

'/' is not a valid resource name character

Is there any idea to make thing consistency?

More info https://developer.android.com/reference/androidx/preference/PreferenceFragmentCompat