when having 2 language sites, Excerpt counts by word in 1 language but counts by character in another language

WordPress 5.2
Plugin:
Post Grid by PickPlugins 2.0.33
Polylang 2.5.3 (Multiple languages plugin)

1. Install 2 plugins "Post Grid by PickPlugins 2.0.33" and "Polylang 2.5.3"
2. Set Polylang to have 2 languages sites EN and TH
3. Create a post in EN. The content is "1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20"
4. Create a post in TH. The content is "1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20"
5. Create a new Post Grid with "flat" layout, observe the excerpt is set to 20
6. Add the Post Grid shortcode to an EN page and TH page.
7. Check the excerpt of the post in EN page, it's shown "1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20"
8. Then change the language to TH check the excerpt of the post in TH, it's shown "1 2 3 4 5 6 7 8 9 10"

I guess this happens because the excerpt of the post in EN counts by word but the excerpt of the post in TH counts by character.
I'd like to have the excerpt in both language to be the same.

Please advise. Thanks.