The meaning of these two words as used in the text you cite (Agile Documentation) is not exactly the same as it has been before the age of computers ; in this text it is specialised to modern text treatment and apparently the established usage in this new field has not yet been recognised in French. A clue that tends to confirm this lacuna in the French text treatment outlook is the lack of a translation into French of the articles of Wikipedia in English for the two words.

Readability

Readability is the ease with which a reader can understand a written text. In natural language, the readability of text depends on its content (the complexity of its vocabulary and syntax) and its presentation (such as typographic aspects like font size, line height, and line length).

Legibility

Legibility is the ease with which a reader can recognize individual characters in text. "The legibility of a typeface is related to the characteristics inherent in its design … which relate to the ability to distinguish one letter from the other."Aspects of type design that affect legibility include "x-height, character shapes, stroke contrast, the size of its counters, serifs or lack thereof, and weight."

 

Legibility is different from readability. Readability is the ease with which a reader can recognize words, sentences, and paragraphs. Legibility is a component of readability. Other typographic factors that affect readability include font choice, point size, kerning, cases used, tracking, line length, leading, and justification.

From these articles it can be seen that readability in the world of text treatment is an all encompassing term that covers all difficulties in the task of absorbing textual information and that legibility is a component of readability. "Readability" is the ease in understanding the text on the level style and syntax on the one hand and on that of presentation on the other, and "legibility" is the ease afforded by the presentation of the text to absorb the content (character shape, type of line (length, height), justification).

From this point of view it is necessary to modify the usual translation of "readability" ("lisibilité"); a good choice (suggested by this answer (user Damien) is "intelligibilité globale"; a translation for "legibility" could then still be "lisibilité" but a more specific term would be "lisibilité matérielle", a term that has not been used, as far as I know, but some such term has become necessary.

A translation of the sentence along the lines of thinking of the quoted articles could then be as follows.

• L'intelligibilité globale c'est une chose, la lisibilité matérielle c'en est une autre.
  (Readability is one thing, legibility another.)

The meaning of these two words as used in the text you cite (Agile Documentation) is not exactly the same as it has been before the age of computers ; in this text it is specialised to modern text treatment and apparently the established usage in this new field has not yet been recognised in French. A clue that tends to confirm this lacuna in the French text treatment outlook is the lack of a translation into French of the articles of Wikipedia in English for the two words.

Readability

Readability is the ease with which a reader can understand a written text. In natural language, the readability of text depends on its content (the complexity of its vocabulary and syntax) and its presentation (such as typographic aspects like font size, line height, and line length).

Legibility

Legibility is the ease with which a reader can recognize individual characters in text. "The legibility of a typeface is related to the characteristics inherent in its design … which relate to the ability to distinguish one letter from the other."Aspects of type design that affect legibility include "x-height, character shapes, stroke contrast, the size of its counters, serifs or lack thereof, and weight."

Legibility is different from readability. Readability is the ease with which a reader can recognize words, sentences, and paragraphs. Legibility is a component of readability. Other typographic factors that affect readability include font choice, point size, kerning, cases used, tracking, line length, leading, and justification.

From these articles it can be seen that readability in the world of text treatment is an all encompassing term that covers all difficulties in the task of absorbing textual information and that legibility is a component of readability. "Readability" is the ease in understanding the text on the level style and syntax on the one hand and on that of presentation on the other, and "legibility" is the ease afforded by the presentation of the text to absorb the content (character shape, type of line (length, height), justification).

From this point of view it is necessary to modify the usual translation of "readability" ("lisibilité"); a good choice (suggested by this answer (user Damien) is "intelligibilité globale"; a translation for "legibility" could then still be "lisibilité" but a more specific term would be "lisibilité matérielle", a term that has not been used, as far as I know, but some such term has become necessary.

A translation of the sentence along the lines of thinking of the quoted articles could then be as follows.

• L'intelligibilité globale c'est une chose, la lisibilité matérielle c'en est une autre.
  (Readability is one thing, legibility another.)