From CSS WG  issue 1517 [1]

This test: http://jsbin.com/botezog/edit?html,output
indicates that 'letter-spacing' is applied to:

* line-right direction in Edge and WebKit.
* the end side of bidi resolved direction in Gecko and Blink.

The CSS Text Level 3[2] defines an algorithm that does not have this problem, but it is currently:
* I can't figure out how to implement it. Raised at CSS WG  issue 1509 .
* May have web-compat problem. Raised at CSS WG  issue 1518 .

[1] https://github.com/w3c/csswg-drafts/issues/1517
[2] https://drafts.csswg.org/css-text-3/#letter-spacing-property
[3] https://github.com/w3c/csswg-drafts/issues/1509
[4] https://github.com/w3c/csswg-drafts/issues/1518
 

From CSS WG 1517 [1]

This test: http://jsbin.com/botezog/edit?html,output
indicates that 'letter-spacing' is applied to:

* line-right direction in Edge and WebKit.
* the end side of bidi resolved direction in Gecko and Blink.

The CSS Text Level 3[2] defines an algorithm that does not have this problem, but it is currently:
* I can't figure out how to implement it. Raised at CSS WG 1509 .
* May have web-compat problem. Raised at CSS WG 1518 .

[1] https://github.com/w3c/csswg-drafts/issues/1517
[2] https://drafts.csswg.org/css-text-3/#letter-spacing-property
[3] https://github.com/w3c/csswg-drafts/issues/1509
[4] https://github.com/w3c/csswg-drafts/issues/1518
 

From CSS WG 1517[1]

This test: http://jsbin.com/botezog/edit?html,output
indicates that 'letter-spacing' is applied to:

* line-right direction in Edge and WebKit.
* the end side of bidi resolved direction in Gecko and Blink.

The CSS Text Level 3[2] defines an algorithm that does not have this problem, but it is currently:
* I can't figure out how to implement it. Raised at CSS WG 1509[3].
* May have web-compat problem. Raised at CSS WG 1518[4].

[1] https://github.com/w3c/csswg-drafts/issues/1517
[2] https://drafts.csswg.org/css-text-3/#letter-spacing-property
[3] https://github.com/w3c/csswg-drafts/issues/1509
[4] https://github.com/w3c/csswg-drafts/issues/1518