Karabiner Umlauts (alt+u ⇒ ü, etc.)
<?xml version="1.0"?>
<root>
<item>
<name>Easy access for Umlauts</name>
<identifier>private.easy_umlaut_access</identifier>
<autogen>
--KeyToKey--
KeyCode::A, ModifierFlag::OPTION_L | ModifierFlag::SHIFT_L,
KeyCode::U, ModifierFlag::OPTION_L, KeyCode::A, ModifierFlag::SHIFT_L
</autogen>
<autogen>
--KeyToKey--
KeyCode::A, ModifierFlag::OPTION_L,
KeyCode::U, ModifierFlag::OPTION_L, KeyCode::A
</autogen>
<autogen>
--KeyToKey--
KeyCode::O, ModifierFlag::OPTION_L | ModifierFlag::SHIFT_L,
KeyCode::U, ModifierFlag::OPTION_L, KeyCode::O, ModifierFlag::SHIFT_L
</autogen>
<autogen>
--KeyToKey--
KeyCode::O, ModifierFlag::OPTION_L,
KeyCode::U, ModifierFlag::OPTION_L, KeyCode::O
</autogen>
<autogen>
--KeyToKey--
KeyCode::U, ModifierFlag::OPTION_L | ModifierFlag::SHIFT_L,
KeyCode::U, ModifierFlag::OPTION_L, KeyCode::U, ModifierFlag::SHIFT_L
</autogen>
<autogen>
--KeyToKey--
KeyCode::U, ModifierFlag::OPTION_L,
KeyCode::U, ModifierFlag::OPTION_L, KeyCode::U
</autogen>
<autogen>
--KeyToKey--
KeyCode::A, ModifierFlag::OPTION_R | ModifierFlag::SHIFT_L,
KeyCode::U, ModifierFlag::OPTION_L, KeyCode::A, ModifierFlag::SHIFT_L
</autogen>
<autogen>
--KeyToKey--
KeyCode::A, ModifierFlag::OPTION_R,
KeyCode::U, ModifierFlag::OPTION_L, KeyCode::A
</autogen>
<autogen>
--KeyToKey--
KeyCode::O, ModifierFlag::OPTION_R | ModifierFlag::SHIFT_L,
KeyCode::U, ModifierFlag::OPTION_L, KeyCode::O, ModifierFlag::SHIFT_L
</autogen>
<autogen>
--KeyToKey--
KeyCode::O, ModifierFlag::OPTION_R,
KeyCode::U, ModifierFlag::OPTION_L, KeyCode::O
</autogen>
<autogen>
--KeyToKey--
KeyCode::U, ModifierFlag::OPTION_R | ModifierFlag::SHIFT_L,
KeyCode::U, ModifierFlag::OPTION_L, KeyCode::U, ModifierFlag::SHIFT_L
</autogen>
<autogen>
--KeyToKey--
KeyCode::U, ModifierFlag::OPTION_R,
KeyCode::U, ModifierFlag::OPTION_L, KeyCode::U
</autogen>
</item>
</root>