Mac OS X Version 10.9.5
Open Office Version 4.1.1

I cannot replicate this bug.
Try #1
Set my machine to Language/Region: United Kingdom
Opened up Open Office Writer
Opened up a new clean document in Writer and the status bar showed English (UK) as the language
I then added a default table of 2 rows, 2 columns to that clean document.  
When I brought the cursor focus inside the cells, it continued to say English(UK) at the bottom of the status bar

I then went into a new clean document and added 5 paragraphs of generated Lorem Ipsum text.
In between two paragraphs I inserted a default table of 2 rows, 2 columns

When I brought the cursor focus inside the cells, it continued to say English(UK) at the bottom of the status bar.
Closed Open Office

Try #2:  
Set my machine back to its default Language/Region: 
Opened Open Office Writer
I opened a new document and set all the text to UK English
Steps:
Menus:
Tools -> Language -> For All Text -> More:
In the Options - Langauge Settings - Languages GUI
Default languages for documents section
Western - Changed from Default - English (USA) to English (UK)

This was confirmed by the bottom status bar showing English (UK)

I then went in the document and added 5 paragraphs of generated Lorem Ipsum text.
In between two paragraphs I inserted a default table of 2 rows, 2 columns

When I brought the cursor focus inside the cells, it continued to say English(UK) at the bottom of the status bar.

I then opened up a clean document, followed the above steps to again set the language to English UK.  I then added a default table of 2 rows, 2 columns to that clean document.  
When I brought the cursor focus inside the cells, it continued to say English(UK) at the bottom of the status bar.

I could reproduce this bug:
When having a document that is not using the default language setting, adding a table will change the language settings within the cells to the system default, instead of inheriting the document’s language setting.



Here my test environment:
•	Mac OS X 10.13
•	OpenOffice 4.1.3 AOO413m1(Build:9783)  -  Rev. 1761381
2016-09-23 02:39:34 (Fri, 23 Sep 2016) – latest officially available version at the time of testing
•	My whole system locale is set to “German (Austria)” which is also the default language setting within open office 

Steps to reproduce the bug:
•	Step 1 – Open a new, empty writer document
•	Now the language setting in the status bar (bottom of the window) will show your default language – German (Austria) in my case
•	Step 2 – Now change the language of the current document by clicking on the status bar and choosing anything else (I chose ”Spanish (Venezuela)” and others for my experiments)
•	Step 3 - Now add a table (no matter with which method, I used the toolbar to add a 2x2 table)
•	The expectation now is that also within the table the language is still set to the custom value selected in step 2 - Spanisch (Venezuela) in my case
•	BUT the language within the table changes back to the system default (German (Austria)). This is a defect in my perspective

Additional comments:
The previous defect reports have been focusing on en-GB and en-US locales, which after my experiments seem to not be the critical values of the involved variables. The defect is rather a more generic one and the involved variables are system default locale and currently selected document locale.

Windows 10 Home Version 1709 OS Build 16299.309
OpenOffice version 4.1.5 (AOO415m1(Build:9789)  -  Rev. 1817496)
System’s language was English (USA) 

Bug was reproduced with the following steps
	1.	Open new OpenOffice Writer document. Observe that language on the status bar at the bottom is “English (USA)”
	2.	Click on “English (USA)” and select “More” from the menu that appears.
	3.	On pop-up, under language change from “English (USA)” to “English (UK)”. 
	4.	Note that language displayed on status bar now says “English (UK)”
	5.	Select “Insert” from toolbar and chose “table”. Select “ok” from the pop-up and see 2x2 table appear. 
	6.	Language within the table cells now displayed as “English (USA)’ on the status bar. 
	7.	When clicking outside the cells, language was “English (UK)”.
 
However, bug was not produced with the following steps
	1. Opened new OpenOffice Writer document
	2. Verified that the language was “English (USA)” was the current language and that the word “colour” gets marked as a misspelling. 
	3. Selected “Tools” from toolbar, then “Options”
	4. Within “Options”, expanded “Language Settings” and selected “Languages”
	5. Under “Default languages for documents”, changed the language under “Western” from “Default – English (USA)” to “English (UK)”. I did not change any other settings. Language on status bar below changed from “English (USA) to “English(UK). 
	6. Observed that typing “colour” in the document does not get marked as a misspelling.
	7. Select “Insert” from toolbar and chose “table”. Selected “ok” from the pop-up and a 2x2 table appeared. Language within table was still “English – UK”

I have successfully reproduced this on a Apache_OpenOffice_4.5.0_Win_x86_install_en-US_1858546.exe night build
Steps to reproduce:
-Changed my system's default language to ENG UK
-Opened up New document  in Open Office Writer
-Changed the Document Language settings from ENG US to Danish 
-Entered a 2*2 table
Observed Results:
I observed that as soon as i entered a table,OO document language changed to ENG-US at the bottom bar of the document 
I also observed that language didn't change when i added just paragraphs ,it changed as soon as i entered a table
I also tried the same steps as described in the original report i.e tried to change the document's language  to ENG UK instead of the Danish and found the same result.
No matter what language you will select in your document it will change to US English after adding  a table

Great news! Congratulations on tracking it down to adding tables - this should make it much easier to fix.