Table column references partial key of table B
One way is to create a domain table for the text keys:

CREATE TABLE TEXT_KEYS
( TEXT_KEY INT NOT NULL PRIMARY KEY ); 

CREATE TABLE Texts
( TEXT_KEY INT NOT NULL REFERENCES TEXT_KEYS (TEXT_KEY)
, [language] [nchar](5) NOT NULL
, [text] [nvarchar](max) NULL
,   CONSTRAINT [PK_Texts] PRIMARY KEY CLUSTERED 
    ( TEXT_KEY ASC, [language] ASC
[...]


Now you can use TEXT_KEY from TEXT_KEYS as a foreign key for your other tables.