UESP mentions in their notes of Erandur:

Despite being a self-proclaimed priest of Mara, Erandur will still invoke Azura's name in combat dialogue like any other Dunmer. Additionally, Erandur does have combat lines referencing Mara ("For Lady Mara!", etc.), but these lines are only heard during the Waking Nightmare quest. It is more likely leaving dialogue mentioning Azura out was an oversight during game development, as Erandur's demeanor when speaking of his devotion to Mara, as well as his mention of having set up a shrine to Mara in Nightcaller Temple, strongly implies he is telling the truth about his Divine conversion.

This mod aims to adress this, by disabling any generic Dark Elf dialogue and restoring the combat lines that are only used during his quest.

This mod should be fully compatible with Denizens of Morthal.

Dialogue lines disabled for Erandur

Any Male Dark Elf lines that are sarcastic/snarky or involve the words "Nerevar", "Azura", "n'wah" and "fetcher".

Other Male Dark Elf NPCs will still use them.

Dialogue lines added/restored for Erandur

Combat starts

• For Lady Mara!
• By Her Benevolence, you shall not stop us!
• Time for your final rest!
• They mustn't stop us!
• We fight till the last!

During combat

• I'll send you to Oblivion!
• This is your final hour!
• Feel the Benevolence of Mara!

When healing him

• Thank you, my child.

Bleedout

• Lady Mara... preserve me...
• I've failed you... forgive me...
• Too much... can't...
• Lady Mara... I await your embrace...
• No... not when we're so close...
• Can't fail now... must hang on...

Combat ends

• So endeth the lesson.
• To Oblivion with you.
• Forgive me, my brother.
• Mara forgives you, my child.

FAQ

Q: ESPFE?
A: Yes.

Q: Is this compatible on a existing save?
A: It should work yes.

Q: Will you make a patch for X?
A: Maybe eventually, but not right now.

Q: Will you port this to <insert other version of Skyrim>?
A: I only support the PC Steam English Special Edition of Skyrim. Any other version I won't support myself. However, I do allow others to
port it to other version at their own responsibility. (see permissions)

Q: I have this cool idea. <insert idea> Will you add this?
A: Maybe. If I like it and doesn't take too much time/effort.

Q: Does this work with AE?
A: Maybe, I don't know. I myself use the "best of both worlds version of the downgrade patcher".