Recently, in many new online software I often see that developers omit articles in short sentences, especially on action buttons or tooltips.
For instance: "Add new task" (not "Add a new task"), "Create project" (not "Create a project"), but often in the same software I can see "Make a copy". What are situations it can be justified?
All three of these examples are correct. Here is an explanation for the difference between "Make a copy" on the one hand, versus "Add new task" and "Create project" on the other hand:
These command labels (or tooltips) are of the form <imperative verb> <object (noun)>.
As our host (Joel Spolsky) has pointed out, "Experienced UI designers literally try to minimize the number of words on dialogs to increase the chances that they will get read."
Some words in English can be either nouns or verbs. On the one hand, "copy" is about equally likely to be a noun or a verb, especially in the context of most computer applications. On the other hand, "task" and "project" are almost always nouns, and only rarely are verbs.
Adverbs make it obvious that a nearby word is an adjective or a verb, not a noun. (Many adverbs end in "ly".)
Some words in English make it obvious that a nearby word is a noun, not a verb. These words include articles like "a" and "the", numbers like "one" and "two", and adjectives like "new". (Many adjectives end in "ous" or "ish".)
Sometimes using an article changes the meaning of a noun. This is not the case in any of these examples.
Getting back to your examples:
"Make a copy" needs the "a" to make it obvious that "copy" is a noun. The user has a 50:50 chance of thinking that "Make copy" is two verbs in a row, not a verb followed by a noun.
"Add new task" has the adjective "new", so it is obvious that "task" is a noun.
The user will probably think that "Make project" is a verb followed by a noun. "Make project" is therefore OK, unless the program uses the word "project" to mean "push something forward" or "perform a map projection". (By the way, the noun "project" and the verb "project" are pronounced differently.)
Firstly, developers are not grammarians. Secondly, if they are writing titles or headlines, the grammar rules are flexible as Damkerng said. The style is refer to as headlinese. Thirdly, at times they try to save space to fit the text in particular field --say some field or text box or things the like.
About the one who wrote it 'make a copy' must have minded the article unlike this programmer here on Magento thread!
people use short world instead long words for easy going. We can see many ad campaign where English words are used in a short form. in the world of SMS and Whatsapp language will be no more. It is a serious concern for grammar lovers.
