Able to reproduce the issue on Mac 10.13.3, Win-10 and Ubuntu 17.10 using chrome reported version #68.0.3440.84 and latest canary #70.0.3516.0.
This is a non-regression issue as it is observed from M60 old builds. 

Hence, marking it as untriaged to get more inputs from dev team.

Thanks...!!

An external contributor is working on this. I'll add an owner once we confirm contributor status.

bool SVGTests::IsValid() 

https://cs.chromium.org/chromium/src/third_party/blink/renderer/core/svg/svg_tests.cc?type=cs&sq=package:chromium&g=0&l=56

requires the systemLanguage langtag (ie, value) to be exactly 2 characters long (so any langtag such as en-US is ignored) and then does the prefix match backward (value is tested as a prefix of user preference rather than user preference is a prefix of value).

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/1f24b02c1e563e405a59d5d44eeb03a6f2c00d59

commit 1f24b02c1e563e405a59d5d44eeb03a6f2c00d59
Author: Fredrik Söderquist <fs@opera.com>
Date: Thu Aug 30 15:29:57 2018

Fix SVG systemLanguage conditional processing

The algorithm that performs the test between browser language preference
and the systemLanguage value has been modified
to implement a language-tag match based on the prefix,
making it consistent with BCP 47's basic filter operation and
as specified in the SVG 1.1 spec.

The previous behavior was:

- Tests whether the value of the attribute (e.g., "en-us") is a prefix
of the user preferred language (e.g., "en")
(which would evaluate to false)

The test was modified to compare in the opposite manner,
now user preferred language must be a prefix of the value.

- If the language tag length was not 2, the language tag
was not matched, (e.g. It did not match "en-us" to "en-us").
This check has been removed.

- The algorithm did not check for a trailing hyphen ("-").
We do not want langtag "it" matching langtag "ita",
but it is ok for "it" to match "it-it".
Now it does.

------------

The algorithm that performs the test between browser language preference
and the systemLanguage value has been modified
to implement a case insensitive language-tag match:

"en" matches "EN".

The previous behavior was case sensitive.

------------

Add Luca Di Domenico to AUTHORS

------------

Bug:  872378 ,  869440 
Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_slimming_paint_v2;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: Ibe767644b5a92e8d79ffe4b7777f5f51851b3883
Reviewed-on: https://chromium-review.googlesource.com/1188314
Commit-Queue: Fredrik Söderquist <fs@opera.com>
Reviewed-by: Fredrik Söderquist <fs@opera.com>
Cr-Commit-Position: refs/heads/master@{#587592}
[modify] https://crrev.com/1f24b02c1e563e405a59d5d44eeb03a6f2c00d59/AUTHORS
[modify] https://crrev.com/1f24b02c1e563e405a59d5d44eeb03a6f2c00d59/third_party/WebKit/LayoutTests/platform/linux/svg/W3C-SVG-1.1/struct-cond-02-t-expected.png
[modify] https://crrev.com/1f24b02c1e563e405a59d5d44eeb03a6f2c00d59/third_party/WebKit/LayoutTests/platform/linux/svg/W3C-SVG-1.1/struct-cond-02-t-expected.txt
[modify] https://crrev.com/1f24b02c1e563e405a59d5d44eeb03a6f2c00d59/third_party/WebKit/LayoutTests/platform/mac/svg/W3C-SVG-1.1/struct-cond-02-t-expected.png
[modify] https://crrev.com/1f24b02c1e563e405a59d5d44eeb03a6f2c00d59/third_party/WebKit/LayoutTests/platform/mac/svg/W3C-SVG-1.1/struct-cond-02-t-expected.txt
[modify] https://crrev.com/1f24b02c1e563e405a59d5d44eeb03a6f2c00d59/third_party/WebKit/LayoutTests/platform/win/svg/W3C-SVG-1.1/struct-cond-02-t-expected.png
[modify] https://crrev.com/1f24b02c1e563e405a59d5d44eeb03a6f2c00d59/third_party/WebKit/LayoutTests/platform/win/svg/W3C-SVG-1.1/struct-cond-02-t-expected.txt
[add] https://crrev.com/1f24b02c1e563e405a59d5d44eeb03a6f2c00d59/third_party/WebKit/LayoutTests/svg/dom/systemLanguage-case-insensitive.html
[add] https://crrev.com/1f24b02c1e563e405a59d5d44eeb03a6f2c00d59/third_party/WebKit/LayoutTests/svg/dom/systemLanguage-langtag-match-prefix.html
[modify] https://crrev.com/1f24b02c1e563e405a59d5d44eeb03a6f2c00d59/third_party/blink/renderer/core/svg/svg_tests.cc

If lang_tag.length() < language.length() then lang_tag does not start with language, and StartsWith... returns false, so lang_tag.length() >= language.length() at that point in time.

Yes, I already realized that and deleted the comment.