MySQL 5.7

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CREATE TABLE codes (id SERIAL, code TEXT, country TEXT);
CREATE TABLE code_translations (id SERIAL, code_id INT, language TEXT, label TEXT);

INSERT INTO codes (id, code, country) VALUES 
    (1, 'A', 'DE'),  
    (2, 'B', 'DE'),
    (3, 'C', 'DE');

INSERT INTO code_translations (code_id, language, label) VALUES
    (1, 'de', 'A-de'),
    (1, 'en', 'A-en'),
    (1, 'fr', 'A-fr'),
    (2, 'de', 'B-de'),
    (2, 'en', 'B-en'),
    (3, 'nl', 'C-nl'),
    (3, 'ru', 'C-ru');
SELECT c.code,
       (
         SELECT ct.label
         FROM code_translations ct
         WHERE ct.code_id = c.id
         ORDER BY FIELD(ct.language, 'en', 'de') DESC
         LIMIT 1
       ) label
FROM codes c


code
label


A
A-de

B
B-de

C
C-nl


SELECT c.code,
       (
         SELECT ct.label
         FROM code_translations ct
         WHERE ct.code_id = c.id
         ORDER BY FIELD(ct.language, 'en', 'fr') DESC
         LIMIT 1
       ) label
FROM codes c


code
label


A
A-fr

B
B-en

C
C-nl


SELECT c.code,
       (
         SELECT ct.label
         FROM code_translations ct
         WHERE ct.code_id = c.id
         ORDER BY FIELD(ct.language, 'en', 'ru') DESC
         LIMIT 1
       ) label
FROM codes c


code
label


A
A-en

B
B-en

C
C-ru