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Server: Microsoft-IIS/8.5
System: Windows NT YDAWBH120 6.3 build 9600 (Windows Server 2012 R2 Standard Edition) AMD64
User: tentjecom_web (0)
PHP: 7.4.14
Disabled: NONE
$ pwd: D:/HostingSpaces/MvAlphen/va-bo.nl/wwwroot/wp-content/plugins/js_composer/locale/
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File: D:/HostingSpaces/MvAlphen/va-bo.nl/wwwroot/wp-content/plugins/js_composer/locale/readme.txt
Official info about translation: http://codex.wordpress.org/Translating_WordPress

In two words: open default.po file and save new copy as js_composer-es_ES.po for Spanish.
And then use translating program to translate it to Spanish language.
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