Developers often use concatenation in string handling: they construct strings from parts in their code at run time (in effect reusing text strings).
However, you are only allowed to use concatenation if the compound parts will not be localized, for example, if the string to be constructed contains a web address. Concatenation is not allowed for strings that need to be localized.
Text fragments are likely to be difficult or even impossible to translate: not only because it is difficult to understand which parts belong together, but also because in most languages, a word needs a different appearance depending on the context. For example:
In some languages, a word can be conjugated or inflected depending on the context. For example, the fragment "New" would look strange and be grammatically incorrect in some contexts.
In languages based on Latin script, capitalization is normally used in the beginning of a sentence. This means a lowercase text fragment ("new" vs. "New") would be orthographically incorrect in some contexts.