How does the kind of language Tom uses as a narrator in The Glass Menagerie by Tennessee Williams differ from that he uses as a character?

As a narrator, Tom is looking back in time, retrospectively. As such, he has had the time to analyze the events of the night when he left the household, and he has been away from his family long enough to look back objectively at the dynamics that were taking place in the Wingfield household.

The tone that he uses as a narrator is, therefore, much more mature, calm, and organized in comparison to the language that he uses "in the moment" as a character.

Clearly, the "Tom" that still lives with Amanda and Laura is a very confused, and a much less mature, man. He is on the brink of making a life-changing event, and he carries with him all the anxiety, angst, frustration, and denial that come with having to make a big decision.

The Tom that still lives in the apartment is someone who is so fed up with life, and so insecure about the changes that he has to make, that he lashes out against the things that he sees as obstacles.

What do you think I’m at? Aren’t I supposed to have any patience to reach the end of, Mother? [[...] It seems unimportant to you, what I’m doing – what I want to do – having a little difference between them!

Look! I’d rather somebody packed up a crowbar and battered out my brains—than go back mornings! I go! Every time you come in yelling that Goddamn ‘Rise and Shine! Rise and Shine!’ I say to myself, ‘How lucky dead people are!’ But I get up.

This happens particularly with Amanda, his mother. Being that she is a possessive woman, unable to move on from the past, and unwilling to make personal changes in view of the changing times, Tom sees her as his principal nemesis. He is trying to become Amanda's literal opposite by trying to move on, trying to change, and trying to adapt to life. The more time he spends near her, the more difficult this becomes. 

Once he is out of the house, however,  time passes, and his emotions neutralize a little bit more compared to when he was at the household. Tom is even willing to find a degree of understanding for his mother and sister, and now sees them as victims of circumstances, and of their own, co-dependent inability to break free and move on from the shadow of the father. 

Therefore, his language is more forgiving, sentimental, nostalgic, composed and even poetic and figurative.

Man is by instinct a lover, a hunter, a fighter, and none of those instincts are given much play at the warehouse.

I didn’t go to the moon – I went much further—for time is the longest distance between two poles. Not long after that I was fired for writing a poem on the lid of a shoe-box. 

Still, the one thing that he hurts for the most is the fact that he could not help his sister become liberated and free. He had to leave her behind in order to save himself. For that reason, his speech will always carry a gravitas that d guilt and the wish to be able to help her in some way.