CREATE TABLE CONTRAGENT (
    CD_ID             BIGINT NOT NULL,
    CD_NAME           VARCHAR(255) NOT NULL, /*WIN1251*/
    CD_ID_CDK         BIGINT NOT NULL /*тип контрагента*/
);

CREATE TABLE LANG (
    ALIAS  VARCHAR(128) NOT NULL,
    ID     BIGINT NOT NULL,
    TEXTU  VARCHAR(4096) CHARACTER SET UNICODE_FSS NOT NULL
);

select cd.cd_name || '/' || l.textu
from contragent cd
left join lang l on l.id = 27004 and l.alias = 'CD_KIND.' || cast(cd.cd_id_cdk as varchar(128))
where cd.cd_id = 123

arithmetic exception, numeric overflow, or string truncation.
Cannot transliterate character between character sets.

select  cd.cd_name  from ...

select  l.textu  from ...

TEXTUTF  VARCHAR(4096) CHARACTER SET UTF8

select cd.cd_name || '/' || l.textutf
from contragent cd
left join lang l on l.id = 27004 and l.alias = 'CD_KIND.' || cast(cd.cd_id_cdk as varchar(128))
where cd.cd_id = 123

arithmetic exception, numeric overflow, or string truncation.
Cannot transliterate character between character sets

Token unknown - line 1, column 40.
charset

TEXTUTF  VARCHAR(4096) CHARACTER SET UTF8