Android - How to change bottom navigation bar text's font family

add the font file in the res/font/ folder to bundle fonts as resources

then

You can change it using style resources.In your styles.xml:

<style name="Widget.BottomNavigationView"     parent="Widget.Design.BottomNavigationView">    <item name="fontFamily">@font/your_font</item></style>

Then apply it as a theme in your view:

<android.support.design.widget.BottomNavigationView    ...    android:theme="@style/Widget.BottomNavigationView"/>

Just checked on my app, it works fine.

reference:https://developer.android.com/guide/topics/ui/look-and-feel/fonts-in-xml.html#fonts-in-code

In your layout:

<com.google.android.material.bottomnavigation.BottomNavigationView    ...    app:itemTextAppearanceActive="@style/BottomNavigationViewTextStyle"    app:itemTextAppearanceInactive="@style/BottomNavigationViewTextStyle"    ... />

In your styles.xml:

<style name="BottomNavigationViewTextStyle">    ...    <item name="android:fontFamily">@font/whatever_font</item>    ...</style>

If you have a CustomFont in "Asset Folder" and you want to set in your "Bottom Navigation" use this code

        public static void persian_iran_font(final Context context, final View v) {            try {                if (v instanceof ViewGroup) {                    ViewGroup vg = (ViewGroup) v;                    for (int i = 0; i < vg.getChildCount(); i++) {                        View child = vg.getChildAt(i);                        persian_iran_font(context, child);                    }                } else if (v instanceof TextView) {                    ((TextView) v).setTypeface(Typeface.createFromAsset(context.getAssets(), "teshrinarmedium.otf"));                }            } catch (Exception e) {            }        }    

And then use methode in your MainActivityLike This

  BottomNavigationView navigation = (BottomNavigationView) findViewById(R.id.navigation);  persian_iran_font(getApplicationContext(), navigation);

kotlin Version

fun persian_iran_font(context: Context, v: View) {    try {        if (v is ViewGroup) {            val vg = v as ViewGroup            for (i in 0 until vg.childCount) {                val child: View = vg.getChildAt(i)                persian_iran_font(context, child)            }        } else if (v is TextView) {            (v as TextView).setTypeface(                Typeface.createFromAsset(                    context.getAssets(),                    "teshrinarmedium.otf"                )            )        }    } catch (e: Exception) {    }}

Goodluck