Two minor changes (in both files).

The reason for specifying ISO 639-1 is that there's also ISO 639-2.
https://en.wikipedia.org/wiki/List_of_ISO_639-1_codes
has 'de' as ISO 639-1 and 'deu', 'ger' as various ISO 639-2 codes, and ISO 639-3.
Additionally https://www.loc.gov/standards/iso639-2/php/English_list.php
there's gsw (Swiss German), nds (Low German), ...

RationaleMCP/0035/SpecificationText.md

@@ -7,7 +7,7 @@ The files to support translation must be provided by the developer of the librar
 Two kind of files have to be provided:
 * a template file `<LibraryName>.pot`. 
 It contains all necessary information to translate all descriptions, but no translations. The pattern `<LibraryName>` denotes the toplevel class name of the library.
-* one file for each supported language with the name `<LibraryName>.<language>.po`. This file is a copy of the associated template file, but extended with the translations in the specified language. The pattern `<language>` stands for the ISO 639 language code, e.g. de or en.
+* one file for each supported language with the name `<LibraryName>.<language>.po`. This file is a copy of the associated template file, but extended with the translations in the specified language. The pattern `<language>` stands for the ISO 639-1 language code, e.g. de or en.
 
 The files consist of a header and a body. All text strings are in double quotes and encoded with UTF-8 characters. Comments start with an `#` and are continued until the end of line. Spaces outside strings are ignored and used as separators. The detailed format of these files is described in [GNU gettext](https://www.gnu.org/software/gettext/manual/gettext.pdf).
 
@@ -78,5 +78,5 @@ The texts in following Modelica constructs should be translated:
 
 C-style and line comments are not translated.
 
-[*To support the translation of that strings a number of free and commercial tools exist in context of GNU gettext. 
+[*To support the translation of these strings a number of free and commercial tools exist in context of GNU gettext. 
 A Modelica tool should provide a function to create the initial template file from an existing Modelica library.*]

chapters/packages.tex

@@ -345,7 +345,7 @@ \section{Multilingual Descriptions}\label{multilingual-descriptions}
 The pattern \filename{<LibraryName>} denotes the toplevel class name of the library.
 \item one file for each supported language with the name \filename{<LibraryName>.<language>.po}.
 This file is a copy of the associated template file, but extended with the translations in the specified language.
-The pattern \filename{<language>} stands for the ISO 639 language code, e.g. de or en.
+The pattern \filename{<language>} stands for the ISO 639-1 language code, e.g. de or en.
 \end{enumerate}
 
 The files consist of a header and a body.
@@ -433,7 +433,7 @@ \section{Multilingual Descriptions}\label{multilingual-descriptions}
 C-style and line comments are not translated.
 
 \begin{nonnormative}
-To support the translation of that strings a number of free and commercial tools exist in context of GNU gettext.
+To support the translation of these strings a number of free and commercial tools exist in context of GNU gettext.
 A Modelica tool should provide a function to create the initial template file from an existing Modelica library.
 \end{nonnormative}