15 Additional Flags were added to the game client in 0.7.8.0, as well as one flag getting replaced.

New Signals:
-Basilisk: +75% to XP per battle, +30% to credits per battle.
-Scylla: +50% to XP per battle, +150% to Commander XP per battle, +25% to credits per battle.
-Leviathan: +50% to XP per battle, +100% to Commander XP per battle, +200% to Free XP earned per battle, +20% to credits per battle.

Flags:
-Pirate Hunter – Tied to an Event for Pirate Day (Sept 19th) (Probably)
-Alaska: Flag for players who have the USS Alaska (Currently on live super-test)
-Le Terrible: Premium Flag for the French T8 Premium Destroyer (Coming Soon™)
-“AL” Flags: Azure Lane Flags, part of the WG/AL cooperative effort, possibly tied to the new Azure Lane camouflages added this patch.
Jolly Roger 6: Commemorative Flag for players Reaching Rank 1 of Ranked Battles for a 10th Time

Replaced:
Purrfurst: The original flag was added in 0.7.3.0, and is now replaced in 0.7.8.0. This flag I am uncertain how is acquired.

W0W54TG4M35C0M
Gives some ingame missions.

9 New additional Flags have been added in the 0.7.7.0 patch.

-Argentina: This will be an optional flag for the Julio, which will be able to choose between this flag or the pan-america flag.
-Jean Bart: Premium flag for the T9 French Battleship Jean Bart
-Prinz Eitel Friedrich: Premium Flag for the upcoming German T6 premium battlecruiser
-AVA Common, Eagles, Sharks: These are event flags tied to the Sharks vs. Eagles game event.
-USS Boise: Premium Flag for the T7 American CL USS Boise.
-Gamescom 2018: Flag for participants of gamescom 2018
-Galleria Gamemaster: No fucking clue, please let me know what this is