This shabbos, the Parasha, Bo, starts with Moshe being told to "Bo El Paroh", "Come to Pharaoh". I don't understand this wording, should it have said "Lech El Paroh", "go to Pharaoh"? Is there a reason why the command was worded that way?
The Zohar (vol. 2 34a) explains (translation from chabad.org):
Rabbi Simeon [bar Yochai] continued: It is now fitting to reveal mysteries connected with that which is above and that which is below. Why is it written, "Come in to Pharaoh"? Ought it not rather to have said, "Go to Pharaoh"? It is to indicate that G-d brought Moses into a chamber within a chamber, into the abode of the supernal mighty serpent that is the soul of Egypt, from whom many lesser serpents emanate. Moses was afraid to approach him, because his roots are in supernal regions, and he only approached his subsidiary streams. When G-d saw that Moses feared the serpent, He said, "Come in to Pharaoh."
God gives this instruction - "בא אל פרעה" - to Moshe preceding three of the Plagues: Frogs (Shemot 7:26), Dead Animals (Shemot 9:1), and Locusts (Shemot 10:1 - your question). According to R' Samson Raphael Hirsch's scheme for understanding the purposes of the Plagues, laid out in his commentary on 7:15, these three plagues, each the second in a group of three, form a group with a particular message to impart, and the use of this command to kick them off fits with that message, just as the introductions to the other two groups of three fit their intended messages.
In R' Hirsch's scheme (which takes its queue from R' Yehuda's famous initialization דצ"ך עד"ש באח"ב), the first nine Plagues can be divided into three sets of three, each of which contained the same three messages in sequence:
גרות - God can make you strangers in your own land at will. How dare you treat others as strangers? (Blood, Wild Beasts, and Hail)
עבדות - God can take away your dignity and property, showing you the emptiness of the pride and masterfulness that owning slaves produced in you. (Frogs, Dead Animals, and Locusts)
ענוי - This is what it feels like to be subjected to unrelenting pain. (Lice, Boils, and Darkness)
(See R' Hirsch's commentary for a full explanation of how each of the Plagues fit into this scheme.)
For the first Plague in each set, God commands Moshe to confront Paraoh at or on the way to the Nile River, using the verbs "לך" (Shemot 7:15) or "התיצב" (Shemot 8:16 and Shemot 9:13). The message here, according to R' Hirsch (at the end of the commentary on 7:15), is "Your future does not depend on the goodwill of the River but on the will of Him Who has sent me." To someone whose royalty, theology, national identity, and economy depended on the stable provision of this river, this gesture was quite alienating, thus fitting with the גרות theme.
The third Plague in each set was meant not to teach a lesson so much as to punish Pharaoh for not listening to the first two lessons as well as for his terrible mistreatment of the Jews. Accordingly, they are not preceded by a confrontation/lesson from Moshe. Instead, God commands Moshe to strike without warning in Shemot 8:12, Shemot 9:8, and Shemot 10:21.
Finally, to the question at hand, in the second Plague in each set, God sends Moshe to Pharaoh with the command "בא אל פרעה," which R' Hirsch translates as "Go in to Pharaoh" (my emphasis) and explains (in his comment on 7:26) "visit him in his palace" (consistent with the interpretation of the Ba'al Haturim cited in these answers and the understanding of Onkelos' translation suggested by this comment). Similar to the way God sets up the confrontations in the first Plagues, these confrontations are also meant to undermine the setting: Moshe goes in to Pharaoh's palace "in the midst of all the splendor" (comment on 10:1) and proceeds to promise, in front of the whole court, a degrading and impovershing Plague. Thus, these three plagues are programmed, starting with the location of their announcements, to cut Pharaoh down from the lofty perch from which he presumed to make other humans into property.
I've no time to check amongst the Acharonim, but so far as the Rishonim are concerned it would appear that the only person to even question the language here is the Baal haTurim (even the Rosh doesn't mention it, and it's not asked by Daat Zkeinim). He merely suggests that telling Moses to "come" is what God does when Moses is supposed to confront the Pharaoh in his house, while telling him to "go" is what God does when Moses is supposed to confront the Pharaoh at the river (7:15). He also suggests that the word בא is used because it has the gematria of 3, alluding to the remaining three plagues.
(As a side note, it's interesting that both Onkelos and "Yonatan" render לך as אזל ("go down") in 7:15, and בא as עול ("go up") in 10:1. Up to you whether or not you want to make something of that).
The Chasam Sofer uses this question to answer another question:
How did Moshe know what plague to bring next? Hashem's words do not mention anything about a plague of locust!
The Chasam Sofer explains that Hashem hinted it to him - take בא, to פרעה in order to place these letters of mine (שתי could mean to place, אות can mean letter) in him - take ב and א, and switch them in to פרעה's name. Since א and ע are vocally interchangeable letters, and so are ב and פ, switch the א in for the ע and the ב in for the פ and you end up with בראה, which are the letters of ארבה.
(for an explanation of why Hashem would tell Moshe in this complicated roundabout way, see R' Y.D. Schlesinger's Shaarei Leil HaSeder)
Rabbi Zamir Kohen explains that "Bo" is used to indicated that HaShem is omnipresent. Were HaShem to use the word "Lekh", it would imply that HaShem is not in the location where He commanded Moshe to go.