如是support 包下的TabLayout 则设置：

<style name="TabLayoutStyle" parent="Widget.Design.TabLayout">
    <item name="tabMaxWidth">@dimen/tab_max_width</item>
    <item name="tabIndicatorColor">@color/black</item>
    <item name="tabIndicatorHeight">2dp</item>
    <item name="tabPaddingStart">8dp</item>
    <item name="tabPaddingEnd">8dp</item>
    <item name="tabBackground">?attr/selectableItemBackground</item>
    <item name="tabTextAppearance">@style/TabTextAppearance</item>
    <item name="tabSelectedTextColor">@android:color/white</item>
</style>

<style name="TabTextAppearance" parent="TextAppearance.Design.Tab">
    <item name="android:textSize">14sp</item>
    <item name="android:textColor">@color/white</item>
    <item name="textAllCaps">false</item>
</style>

<android.support.design.widget.TabLayout
    style="@style/TabLayoutStyle"
    android:id="@+id/tabLayout"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"/>

如是com.google.android.material.tabs.TabLayout 包下的TabLayout 则设置：

<style name="customTabLayout" parent="Widget.Design.TabLayout">
    <item name="tabTextAppearance">@style/TabTextAppearance</item>
</style>

<style name="TabTextAppearance" parent="@android:style/TextAppearance.Widget.TabWidget">
    <item name="android:textAllCaps">false</item>
</style>

<com.google.android.material.tabs.TabLayout
    android:id="@+id/tab_layout"
    style="@style/customTabLayout"
    android:layout_width="match_parent"
    android:layout_height="wrap_content" />

或：

<style name="TabTextAppearance" parent="TextAppearance.Design.Tab">
    <item name="textAllCaps">false</item>
</style>

<com.google.android.material.tabs.TabLayout
    android:id="@+id/tab_layout"
    app:tabTextAppearance="@style/TabTextAppearance"
    android:layout_width="match_parent"
    android:layout_height="wrap_content" />