Use textAlignment + gravity. TextAlignment was only added in API 17.

app/src/main/res/layout/app_details2_donate.xml

@@ -16,6 +16,7 @@
         android:layout_height="wrap_content"
         android:textSize="15sp"
         android:textAlignment="center"
+        android:gravity="center"
         tools:text="F-Droid is created by F-Droid Limited and Contributors. Buy them a coffee!"
         android:layout_marginBottom="12dp" />
 

app/src/main/res/layout/installed_apps_layout.xml

@@ -38,6 +38,7 @@
         app:layout_constraintRight_toRightOf="parent"
         android:padding="16dp"
         android:textAlignment="center"
+        android:gravity="center"
         android:textColor="#424242"
         android:textSize="14sp"
         android:text="Tap and hold on an app for more options"

app/src/main/res/layout/main_tab_swap.xml

@@ -18,6 +18,7 @@
         android:layout_marginTop="48dp"
         android:text="@string/nearby_splash__download_apps_from_people_nearby"
         android:textAlignment="center"
+        android:gravity="center"
         android:textSize="20sp"
         android:textColor="#4a4a4a"
         app:layout_constraintLeft_toLeftOf="parent"
@@ -42,6 +43,7 @@
         tools:text="@string/nearby_splash__both_parties_need_fdroid"
         android:textSize="15sp"
         android:textAlignment="center"
+        android:gravity="center"
         android:textColor="#5B5B5B"
         app:layout_constraintTop_toBottomOf="@+id/button"
         app:layout_constraintRight_toRightOf="parent"

app/src/main/res/layout/swap_connecting.xml

@@ -11,10 +11,10 @@
             android:id="@+id/heading"
             android:layout_width="match_parent"
             android:layout_height="wrap_content"
-            android:gravity="center"
             android:textSize="20sp"
             android:padding="30dp"
             android:textAlignment="center"
+            android:gravity="center"
             tools:text="Connecting with Nexus 4"
             tools:ignore="UnusedAttribute" />
 
@@ -30,6 +30,7 @@
             android:id="@+id/error"
             android:textSize="20sp"
             android:textAlignment="center"
+            android:gravity="center"
             android:text="@string/swap_connection_misc_error"
             android:visibility="gone"
             android:padding="30dp"

app/src/main/res/values-v17/styles.xml

@@ -15,19 +15,23 @@
 
     <style name="SwapTheme.AppList.SwapSuccess" parent="SwapTheme.AppList.SwapSuccessBase">
         <item name="android:textAlignment">center</item>
+        <item name="android:gravity">center</item>
         <item name="android:fontFamily">sans-serif-light</item>
     </style>
 
     <style name="SwapTheme.AppList.SwapSuccessDetails" parent="SwapTheme.AppList.SwapSuccessDetailsBase">
         <item name="android:textAlignment">center</item>
+        <item name="android:gravity">center</item>
     </style>
 
     <style name="SwapTheme.StartSwap.MainText" parent="SwapTheme.StartSwap.MainTextBase">
         <item name="android:textAlignment">center</item>
+        <item name="android:gravity">center</item>
     </style>
 
     <style name="SwapTheme.Wizard.Text" parent="SwapTheme.Wizard.TextBase">
         <item name="android:textAlignment">center</item>
+        <item name="android:gravity">center</item>
     </style>
 
     <style name="SwapTheme.Wizard.MainText" parent="SwapTheme.Wizard.MainTextBase">