missing "but"  -- (MW) The untranslated word "but" means "but", "however" and "on the other hand". Since it always falls in the second position, translating it as "however" often captures its feeling better.

When -- The Greek word translated as "when" introduces a phrase that explains a certain condition so "whenever" or "since."

you -- This is from the second-person, plural form of the verb.

see -- The verb translated as "ye shall see" means "to see" but it is used like we use the word "see" to mean "to know" or "to perceive". This verb is not the future tense, but in the form of possibility that indicates something that could happen at any time.

Jerusalem  -- The word "Jerusalem" denotes the city or its inhabitants. Two different forms of this word appear in the NT.  This version is used most heavily in Luke, mostly in his narration, but a few times in Christ's words. It seems to be the more formally Greek version of the name.

being -- This helping verb "be" indicates that the verb is passive. Helping or auxiliary verbs are needed to translate the Greek verb forms into English. The form is a participle which accounts for the "-ing."

surrounded -- "Surrounded" is from a verb used only where that means to "encircle" or "surround". It is in the form of an adjective.

by -- The word translated as "by" primarily means "by", "under" or "with" (with the genitive and a passive verb). Its primary meaning is "under" both in the sense of moving under, being under, and being under different forms of compulsion.

armies -- (CW) "Armies" is another unique word that means "camp" and "encampment". This is not the word usually translated as "armies".

missing "then  "  -- (MW) The untranslated word "then" means "at this time" or "then". 

will -- (CW) This helping verb "will" does not indicate the future tense, but that the verb describes a possibility, the subjunctive voice. A "might" or "should" in English is more appropriate, but is assumed in an "if/when/whoever/except" clause such as here. Helping verbs are not needed in Greek since the main verb carries this information in its form.

its -- The word translated as "its" is the Greek word commonly translated as third-person pronouns in English.  The word means "the same" when used as an adjective. In the adverbial form, it  means "just here" or "exactly there".

missing "the/this"  -- (MW) The untranslated word is the Greek definite article, "the", which usually precedes a noun or changes the word it precedes (adjective, infinitive, participle, etc.) to act like a noun. The Greek article is much closer to our demonstrative pronouns ("this", "that", "these" and "those"). See this article for more. 

desolation --  "Desolation" is from a Greek word that means "making desolate", the idea of "being stripped bare" and being abandoned or deserted. It is in the possessive form. It too is from the Septuagint, but it appears elsewhere in Greek literature. Here, the Hebrew source word means "to be desolate", "to be deflowered", "to stun", "to be appalled", "to devastate", "to ravage", "to cause horror" and "to cause oneself ruin". When Christ refers to the "desert" or "wilderness" he uses the noun form of this word. This word is used only three times in the Gospels usually referring to a verse in Daniel.

is -- (WT) This helping verb indicates the present tense of the verb. This verb is in the past, perfect tense so "has" is correct.  

near -- The word translated as "is near" is the verb form of an adverb "near" in space, time, and relationships. In English, we would say "nears" or, in the form here, "has neared", but that doesn't quite work so perhaps "has gotten close" or, in the case of time, "is nearly here".