SQLite 3.16

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WITH words AS (
      select 1 as id, 'Cat' as word, 'ENG' as lang union all
      select 2, 'Kot', 'POL' union all
      select 3, 'Katze', 'GER'
     ),
     connections as (
      select 1 as id, 1 as word_a, 2 as word_b union all
      select 2 as id, 1 as word_a, 3 as word_b
     ),
     connections2 as (
      select c.word_a as id_a, c.word_b as id_b, wa.lang as lang_a, wb.lang as lang_b
      from connections c join
           words wa
           on c.word_a = wa.id join
           words wb
           on c.word_b = wb.id
      union  -- remove duplicates
      select c.word_b, c.word_a, wb.lang as lang_a, wa.lang as lang_b
      from connections c join
           words wa
           on c.word_a = wa.id join
           words wb
           on c.word_b = wb.id
     ),
     cte as (
      select id as pol_word, id as other_word, 'POL' as lang, 1 as lev, ',POL,' as langs
      from words
      where lang = 'POL'
      union all
      select cte.pol_word, c2.id_b, c2.lang_b, lev + 1, langs || c2.lang_b || ','
      from cte join
           connections2 c2
           on cte.lang = c2.lang_a
      where langs not like '%,' || c2.lang_b || ',%' or c2.lang_b = 'GER'
     ) 
select *
from cte

pol_word	other_word	lang	lev	langs
2	2	POL	1	,POL,
2	1	ENG	2	,POL,ENG,
2	3	GER	3	,POL,ENG,GER,